Cristos Goodrow: YouTube Algorithm
嘉宾：Cristos Goodrow
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§01Transcript · 00:00–14:37
The following is a conversation with Christos Goudreau,
Vice President of Engineering at Google and Head of Search and Discovery at YouTube,
also known as the YouTube Algorithm.
YouTube has approximately 1.9 billion users,
and every day people watch over 1 billion hours of YouTube video.
It is the second most popular search engine behind Google itself.
For many people, it is not only a source of entertainment,
but also how we learn new ideas from math and physics videos to podcasts to debates, opinions,
ideas from out of the box thinkers and activists on some of the most tense,
challenging, and impactful topics in the world today.
YouTube and other content platforms receive criticism from both viewers and creators,
as they should, because the engineering task before them is hard, and they don't always
succeed, and the impact of their work is truly world changing.
To me, YouTube has been an incredible wellspring of knowledge.
I've watched hundreds, if not thousands, of lectures that changed the way I see
many fundamental ideas in math, science, engineering, and philosophy.
But it does put a mirror to ourselves, and keeps the responsibility of the steps we take
in each of our online educational journeys into the hands of each of us.
The YouTube algorithm has an important role in that journey of helping us find new,
exciting ideas to learn about.
That's a difficult and an exciting problem for an artificial intelligence system.
As I've said in lectures and other forums, recommendation systems will be one of the
most impactful areas of AI in the 21st century, and YouTube is one of the biggest
recommendation systems in the world.
This is the Artificial Intelligence Podcast.
If you enjoy it, subscribe on YouTube, give it five stars on Apple Podcast, follow on
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And now, here's my conversation with Christos Goudreau.
YouTube is the world's second most popular search engine, behind Google, of course.
We watch more than 1 billion hours of YouTube videos a day, more than Netflix and Facebook
video combined.
YouTube creators upload over 500,000 hours of video every day.
Average lifespan of a human being, just for comparison, is about 700,000 hours.
So, what's uploaded every single day is just enough for a human to watch in a lifetime.
So, let me ask an absurd philosophical question.
If from birth, when I was born, and there's many people born today with the internet,
I watched YouTube videos nonstop, do you think there are trajectories through YouTube video
space that can maximize my average happiness, or maybe education, or my growth as a human
being?
I think there are some great trajectories through YouTube videos, but I wouldn't recommend
that anyone spend all of their waking hours or all of their hours watching YouTube.
I mean, I think about the fact that YouTube has been really great for my kids, for instance.
My oldest daughter, she's been watching YouTube for several years.
She watches Tyler Oakley and the Vlogbrothers, and I know that it's had a very profound and
positive impact on her character.
And my younger daughter, she's a ballerina, and her teachers tell her that YouTube is
a huge advantage for her because she can practice a routine and watch professional dancers do
that same routine and stop it and back it up and rewind and all that stuff, right?
So, it's been really good for them.
And then even my son is a sophomore in college.
He got through his linear algebra class because of a channel called Three Blue, One Brown,
which helps you understand linear algebra, but in a way that would be very hard for anyone
to do on a whiteboard or a chalkboard.
And so, I think that those experiences, from my point of view, were very good.
And so, I can imagine really good trajectories through YouTube, yes.
Have you looked at, do you think of broadly about that trajectory over a period?
Because YouTube has grown up now.
So, over a period of years, you just kind of gave a few anecdotal examples, but I used
to watch certain shows on YouTube.
I don't anymore.
I've moved on to other shows.
Ultimately, you want people to, from YouTube's perspective, to stay on YouTube, to grow as
human beings on YouTube.
So, you have to think not just what makes them engage today or this month, but what
makes them engage today or this month, but also for a period of years.
Absolutely.
That's right.
I mean, if YouTube is going to continue to enrich people's lives, then it has to grow
with them, and people's interests change over time.
And so, I think we've been working on this problem, and I'll just say it broadly as
like how to introduce diversity and introduce people who are watching one thing to something
else they might like.
We've been working on that problem all the eight years I've been at YouTube.
It's a hard problem because, I mean, of course, it's trivial to introduce diversity
that doesn't help.
Yeah, just add a random video.
I could just randomly select a video from the billions that we have.
It's likely not to even be in your language.
So, the likelihood that you would watch it and develop a new interest is very, very low.
And so, what you want to do when you're trying to increase diversity is find something that
is not too similar to the things that you've watched, but also something that you might
be likely to watch.
And that balance, finding that spot between those two things is quite challenging.
So, the diversity of content, diversity of ideas, it's a really difficult, it's a thing
like that's almost impossible to define, right?
Like, what's different?
So, how do you think about that?
So, two examples is I'm a huge fan of Three Blue One Brown, say, and then one diversity.
I wasn't even aware of a channel called Veritasium, which is a great science, physics, whatever
channel.
So, one version of diversity is showing me Derek's Veritasium channel, which I was really
excited to discover.
I actually now watch a lot of his videos.
Okay, so you're a person who's watching some math channels and you might be interested
in some other science or math channels.
So, like you mentioned, the first kind of diversity is just show you some things from
other channels that are related, but not just, you know, not all the Three Blue One Brown
channel, throw in a couple others.
So, that's maybe the first kind of diversity that we started with many, many years ago.
Taking a bigger leap is about, I mean, the mechanisms we use for that is we basically
cluster videos and channels together, mostly videos.
We do almost everything at the video level.
And so, we'll make some kind of a cluster via some embedding process and then measure
what is the likelihood that users who watch one cluster might also watch another cluster
that's very distinct.
So, we may come to find that people who watch science videos also like jazz.
This is possible, right?
And so, because of that relationship that we've identified through the embeddings and
then the measurement of the people who watch both, we might recommend a jazz video once
in a while.
So, there's this cluster in the embedding space of jazz videos and science videos.
And so, you kind of try to look at aggregate statistics where if a lot of people that jump
from science cluster to the jazz cluster tend to remain as engaged or become more engaged,
then that means those two, they should hop back and forth and they'll be happy.
Right.
There's a higher likelihood that a person who's watching science would like jazz than
the person watching science would like, I don't know, backyard railroads or something
else, right?
And so, we can try to measure these likelihoods and use that to make the best recommendation
we can.
So, okay.
So, we'll talk about the machine learning of that, but I have to linger on things that
neither you or anyone have an answer to.
There's gray areas of truth, which is, for example, now I can't believe I'm going there,
but politics.
It happens so that certain people believe certain things and they're very certain about
them.
Let's move outside the red versus blue politics of today's world, but there's different ideologies.
For example, in college, I read quite a lot of Ayn Rand I studied, and that's a particular
philosophical ideology I found interesting to explore.
Okay.
So, that was that kind of space.
I've kind of moved on from that cluster intellectually, but it nevertheless is an interesting cluster.
I was born in the Soviet Union.
Socialism, communism is a certain kind of political ideology that's really interesting
to explore.
Again, objectively, there's a set of beliefs about how the economy should work and so on.
And so, it's hard to know what's true or not in terms of people within those communities
are often advocating that this is how we achieve utopia in this world, and they're pretty
certain about it.
So, how do you try to manage politics in this chaotic, divisive world?
Not positive or any kind of ideas in terms of filtering what people should watch next
and in terms of also not letting certain things be on YouTube.
This is an exceptionally difficult responsibility.
Well, the responsibility to get this right is our top priority.
And the first comes down to making sure that we have good, clear rules of the road, right?
Like, just because we have freedom of speech doesn't mean that you can literally say anything,
right?
Like, we as a society have accepted certain restrictions on our freedom of speech.
There are things like libel laws and things like that.
And so, where we can draw a clear line, we do, and that's what we do.
We draw a clear line, we do, and we continue to evolve that line over time.
However, as you pointed out, wherever you draw the line, there's going to be a border
line.
And in that border line area, we are going to maybe not remove videos, but we will try
to reduce the recommendations of them or the proliferation of them by demoting them.
Alternatively, in those situations, try to raise what we would call authoritative or
credible sources of information.
So, we're not trying to, I mean, you mentioned Ayn Rand and communism.
Those are two valid points of view that people are going to debate and discuss.
And of course, people who believe in one or the other of those things are going to try
to persuade other people to their point of view.
And so, we're not trying to settle that or choose a side or anything like that.
What we're trying to do is make sure that the people who are expressing those point
of view and offering those positions are authoritative and credible.
So, let me ask a question about people I don't like personally.
You heard me.
I don't care if you leave comments on this.
But sometimes, they're brilliantly funny, which is trolls.
So, people who kind of mock, I mean, the internet is full, Reddit of mock style
comedy where people just kind of make fun of, point out that the emperor has no clothes.
And there's brilliant comedy in that, but sometimes it can get cruel and mean.
So, on that, on the mean point, and sorry to look at the comments, but I'm going to
and sorry to linger on these things that have no good answers.
But actually, I totally hear you that this is really important that you're trying to
solve it.
But how do you reduce the meanness of people on YouTube?
I understand that anyone who uploads YouTube videos has to become resilient to a certain
amount of meanness.
Like I've heard that from many creators.
§02Transcript · 14:37–31:01
And we are trying in various ways, comment ranking, allowing certain features to block
people, to reduce or make that meanness or that trolling behavior less effective on YouTube.
Yeah.
And so, I mean, it's very important, but it's something that we're going to keep having
to work on and as we improve it, like maybe we'll get to a point where people don't have
to suffer this sort of meanness when they upload YouTube videos.
I hope we do, but it just does seem to be something that you have to be able to deal
with as a YouTube creator nowadays.
Do you have a hope that, so you mentioned two things that I kind of agree with.
So there's like a machine learning approach of ranking comments based on whatever, based
on how much they contribute to the healthy conversation.
Let's put it that way.
Then the other is almost an interface question of how do you, how does the creator filter?
So block or how does, how do humans themselves, the users of YouTube manage their own conversation?
Do you have hope that these two tools will create a better society without limiting freedom
of speech too much, without sort of attacking, even like saying that people, what do you
mean limiting, sort of curating speech?
I mean, I think that that overall is our whole project here at YouTube.
Right.
Like we fundamentally believe and I personally believe very much that YouTube can be great.
It's been great for my kids.
I think it can be great for society.
But it's absolutely critical that we get this responsibility part right.
And that's why it's our top priority.
Susan Wojcicki, who's the CEO of YouTube, she says something that I personally find
very inspiring, which is that we want to do our jobs today in a manner so that people
20 and 30 years from now will look back and say, YouTube, they really figured this out.
They really found a way to strike the right balance between the openness and the value
that the openness has and also making sure that we are meeting our responsibility to
users in society.
So the burden on YouTube actually is quite incredible.
And the one thing that people don't give enough credit to the seriousness and the magnitude
of the problem, I think.
So I personally hope that you do solve it because a lot is in your hand, a lot is riding
on your success or failure.
So it's besides, of course, running a successful company, you're also curating the content
of the internet and the conversation on the internet.
That's a powerful thing.
So one thing that people wonder about is how much of it can be solved with pure machine
learning.
So looking at the data, studying the data and creating algorithms that curate the comments,
curate the content, and how much of it needs human intervention, meaning people here at
YouTube in a room sitting and thinking about what is the nature of truth, what are the
ideals that we should be promoting, that kind of thing.
So algorithm versus human input, what's your sense?
I mean, my own experience has demonstrated that you need both of those things.
Algorithms, I mean, you're familiar with machine learning algorithms and the thing
they need most is data and the data is generated by humans.
And so, for instance, when we're building a system to try to figure out which are the
videos that are misinformation or borderline policy violations, well, the first thing we
need to do is get human beings to make decisions about which of those videos are in which category.
And then we use that data and basically take that information that's determined and governed
by humans and extrapolate it or apply it to the entire set of billions of YouTube videos.
And we couldn't get to all the videos on YouTube well without the humans, and we couldn't use
the humans to get to all the videos of YouTube.
So there's no world in which you have only one or the other of these things.
And just as you said, a lot of it comes down to people at YouTube spending a lot of time
trying to figure out what are the right policies, what are the outcomes based on those policies,
are they the kinds of things we want to see?
And then once we kind of get an agreement or build some consensus around what the policies
are, well, then we've got to find a way to implement those policies across all of YouTube.
And that's where both the human beings, we call them evaluators or reviewers, come into
play to help us with that.
And then once we get a lot of training data from them, then we apply the machine learning
techniques to take it even further.
Do you have a sense that these human beings have a bias in some kind of direction?
I mean, that's an interesting question.
We do sort of in autonomous vehicles and computer vision in general, a lot of annotation, and
we rarely ask what bias do the annotators have.
Even in the sense that they're better at annotating certain things than others.
For example, people are much better at, for example, at writing, they're much better at
or much better at annotating segmentation at segmenting cars in a scene versus segmenting
bushes or trees.
There's specific mechanical reasons for that, but also because it's semantic gray area.
And just for a lot of reasons, people are just terrible at annotating trees.
Okay, so in the same kind of sense, do you think of, in terms of people reviewing videos
or annotating the content of videos, is there some kind of bias that you're aware of or
seek out in that human input?
Well, we take steps to try to overcome these kinds of biases or biases that we think would
be problematic.
So for instance, like we ask people to have a bias towards scientific consensus.
That's something that we instruct them to do.
We ask them to have a bias towards demonstration of expertise or credibility or authoritativeness.
But there are other biases that we want to make sure to try to remove.
And there's many techniques for doing this.
One of them is you send the same thing to be reviewed to many people.
And so, that's one technique.
Another is that you make sure that the people that are doing these sorts of tasks, that
these sorts of tasks are from different backgrounds and different areas of the United States or
of the world.
But then, even with all of that, it's possible for certain kinds of what we would call unfair
biases to creep into machine learning systems, primarily, as you said, because maybe the
training data itself comes in in a biased way.
So, we also have worked very hard on improving the machine learning systems to remove and
reduce unfair biases when it goes against or involves some protected class, for instance.
Thank you for exploring with me some of the more challenging things.
I'm sure there's a few more that we'll jump back to.
But let me jump into the fun part, which is maybe the basics of the quote, unquote, YouTube
algorithm.
What does the YouTube algorithm look at to make recommendation for what to watch next?
And it's from a machine learning perspective.
Or when you search for a particular term, how does it know what to show you next?
Because it seems to, at least for me, do an incredible job of both.
Well, that's kind of you to say.
It didn't used to do a very good job, but it's gotten better over the years.
Even I observed that it's improved quite a bit.
Those are two different situations.
Like when you search for something, YouTube uses the best technology we can get from Google
to make sure that the YouTube search system finds what someone's looking for.
And of course, the very first things that one thinks about is, okay, well, does the
word occur in the title, for instance?
But there are much more sophisticated things where we're mostly trying to do some syntactic
match or maybe a semantic match based on words that we can add to the document itself.
For instance, maybe is this video watched a lot after this query?
That's something that we can observe and then as a result, make sure that that document
would be retrieved for that query.
Now, when you talk about what kind of videos would be recommended to watch next, that's
something, again, we've been working on for many years and probably the first real attempt
to do that well was to use collaborative filtering.
Can you describe what collaborative filtering is?
Sure.
It's just basically what we do is we observe which videos get watched close together by
the same person.
And if you observe that and if you can imagine creating a graph where the videos that get
watched close together by the most people are very close to one another in this graph
and videos that don't frequently get watched close together by the same person or the same
people are far apart, then you end up with this graph that we call the related graph
that basically represents videos that are very similar or related in some way.
And what's amazing about that is that it puts all the videos that are in the same
language together, for instance, and we didn't even have to think about language.
It just does it, right?
And it puts all the videos that are about sports together and it puts most of the music
videos together and it puts all of these sorts of videos together just because that's sort
of the way the people using YouTube behave.
So that already cleans up a lot of the problem.
It takes care of the lowest hanging fruit, which happens to be a huge one of just managing
these millions of videos.
That's right.
I remember a few years ago I was talking to someone who was trying to propose that we
do a research project concerning people who are bilingual, and this person was making
this proposal based on the idea that YouTube could not possibly be good at recommending
videos well to people who are bilingual.
And so she was telling me about this and I said, well, can you give me an example of
what problem do you think we have on YouTube with the recommendations?
And so she said, well, I'm a researcher in the US and when I'm looking for academic
topics, I want to see them in English.
And so she searched for one, found a video, and then looked at the watch next suggestions
and they were all in English.
And so she said, oh, I see.
YouTube must think that I speak only English.
And so she said, now I'm actually originally from Turkey and sometimes when I'm cooking,
let's say I want to make some baklava, I really like to watch videos that are in Turkish.
And so she searched for a video about making the baklava and then selected it and it was
in Turkish and the watch next recommendations were in Turkish.
And she just couldn't believe how this was possible and how is it that you know that
I speak both these two languages and put all the videos together?
And it's just as a sort of an outcome of this related graph that's created through
collaborative filtering.
So for me, one of my huge interests is just human psychology, right?
And that's such a powerful platform on which to utilize human psychology to discover what
people, individual people want to watch next.
But it's also be just fascinating to me.
You know, I've, Google search has ability to look at your own history and I've done
that before, just, just what I've searched three years for many, many years.
And it's fascinating picture of who I am actually.
And I don't think anyone's ever summarized.
I personally would love that.
A summary of who I am as a person on the internet to me, because I didn't get a reply
of who I am as a person on the internet to me, because I think it reveals, I think it
puts a mirror to me or to others.
You know, that's actually quite revealing and interesting, you know, just the, maybe
in the number of, it's a joke, but not really is the number of cat videos I've watched or
videos of people falling, you know, stuff that's absurd, that kind of stuff.
It's really interesting.
And of course it's really good for the machine learning aspect to, to show, to figure out
what to show next.
But it's interesting.
Have you just as a tangent played around with the idea of giving a map to people sort of,
as opposed to just using this information to show what's next, showing them here are
the clusters you've loved over the years kind of thing?
Well, we do provide the history of all the videos that you've watched.
Yes.
So you can definitely search through that and look through it and search through it
to see what it is that you've been watching on YouTube.
We have actually in various times experimented with this sort of cluster idea, finding ways
to demonstrate or show people what topics they've been interested in or what clusters
they've watched from.
It's interesting that you bring this up because in some sense, the way the recommendation
system of YouTube sees a user is exactly as the history of all the videos they've
watched on YouTube.
And so you can think of yourself or any user on YouTube as kind of like a DNA strand of
all your videos, right?
That sort of represents you, you can also think of it as maybe a vector in the space
of all the videos on YouTube.
And so now once you think of it as a vector in the space of all the videos on YouTube,
then you can start to say, okay, well, which other vectors are close to me and to my vector?
And that's one of the ways that we generate some diverse recommendations is because you're
like, okay, well, these people seem to be close with respect to the videos they've
watched on YouTube, but here's a topic or a video that one of them has watched and
enjoyed, but the other one hasn't, that could be an opportunity to make a good recommendation.
§03Transcript · 31:01–43:51
I got to tell you, I mean, I know I'm going to ask for things that are impossible, but
I would love to cluster than human beings.
I would love to know who has similar trajectories as me, because you probably would want to
hang out, right?
There's a social aspect there, like actually finding some of the most fascinating people
I find on YouTube, but have like no followers and I start following them and they create
incredible content and on that topic, I just love to ask, there's some videos that just
blow my mind in terms of quality and depth and just in every regard are amazing videos
and they have like 57 views, okay?
How do you get videos of quality to be seen by many eyes?
So the measure of quality, is it just something, yeah, how do you know that something is good?
Well, I mean, I think it depends initially on what sort of video we're talking about.
So in the realm of, let's say you mentioned politics and news, in that realm, you know,
quality news or quality journalism relies on having a journalism department, right?
Like you have to have actual journalists and fact checkers and people like that and so
in that situation and in others, maybe science or in medicine, quality has a lot to do with
the authoritativeness and the credibility and the expertise of the people who make the
video.
Now, if you think about the other end of the spectrum, you know, what is the highest quality
prank video or what is the highest quality Minecraft video, right?
That might be the one that people enjoy watching the most and watch to the end or it might
be the one that when we ask people the next day after they watched it, were they satisfied
with it?
And so we in, especially in the realm of entertainment, have been trying to get at better and better
measures of quality or satisfaction or enrichment since I came to YouTube.
And we started with, well, you know, the first approximation is the one that gets more views.
But you know, we both know that things can get a lot of views and not really be that
high quality, especially if people are clicking on something and then immediately realizing
that it's not that great and abandoning it.
And that's why we moved from views to thinking about the amount of time people spend watching
it with the premise that like, you know, in some sense, the time that someone spends watching
a video is related to the value that they get from that video.
It may not be perfectly related, but it has something to say about how much value they
get.
But even that's not good enough, right?
Because I myself have spent time clicking through channels on television late at night
and ended up watching Under Siege 2 for some reason I don't know.
And if you were to ask me the next day, are you glad that you watched that show on TV
last night?
I'd say, yeah, I wish I would have gone to bed or read a book or almost anything else,
really.
And so that's why some people got the idea a few years ago to try to survey users afterwards.
And so we get feedback data from those surveys and then use that in the machine learning
system to try to not just predict what you're going to click on right now, what you might
watch for a while, but what when we ask you tomorrow, you'll give four or five stars to.
So just to summarize, what are the signals from a machine learning perspective that a
user can provide?
So you mentioned just clicking on the video views, the time watched, maybe the relative
time watched, the clicking like and dislike on the video, maybe commenting on the video.
All of those things.
All of those things.
And then the one I wasn't actually quite aware of, even though I might have engaged in it
is a survey afterwards, which is a brilliant idea.
Is there other signals?
I mean, that's already a really rich space of signals to learn from.
Is there something else?
Well, you mentioned commenting, also sharing the video.
If you think it's worthy to be shared with someone else you know.
Within YouTube or outside of YouTube as well?
Either.
Let's see, you mentioned like, dislike.
Like and dislike.
How important is that?
It's very important, right?
We want, it's predictive of satisfaction.
But it's not perfectly predictive.
Subscribe.
If you subscribe to the channel of the person who made the video, then that also is a piece
of information and it signals satisfaction.
Although over the years, we've learned that people have a wide range of attitudes about
what it means to subscribe.
We would ask some users who didn't subscribe very much, but they watched a lot from a few
channels.
We'd say, well, why didn't you subscribe?
And they would say, well, I can't afford to pay for anything.
We tried to let them understand like, actually it doesn't cost anything.
It's free.
It just helps us know that you are very interested in this creator.
But then we've asked other people who subscribe to many things and don't really watch any
of the videos from those channels.
And we say, well, why did you subscribe to this if you weren't really interested in any
more videos from that channel?
And they might tell us, well, I just, you know, I thought the person did a great job
and I just want to kind of give them a high five.
And so.
Yeah.
That's where I sit.
I go to channels where I just, this person is amazing.
I like this person.
But then I like this person and I really want to support them.
That's how I click subscribe.
Even though I mean never actually want to click on their videos when they're releasing
it.
I just love what they're doing.
And it's maybe outside of my interest area and so on, which is probably the wrong way
to use the subscribe button.
But I just want to say congrats.
This is great work.
Well, so you have to deal with all the space of people that see the subscribe button is
totally different.
That's right.
And so, you know, we can't just close our eyes and say, sorry, you're using it wrong.
You know, we're not going to pay attention to what you've done.
We need to embrace all the ways in which all the different people in the world use the
subscribe button or the like and the dislike button.
So in terms of signals of machine learning, using for the search and for the recommendation,
you've mentioned title.
So like metadata, like text data that people provide description and title and maybe keywords.
Maybe you can speak to the value of those things in search and also this incredible
fascinating area of the content itself.
So the video content itself, trying to understand what's happening in the video.
So YouTube released a data set that, you know, in the machine learning computer vision world,
this is just an exciting space.
How much is that currently?
How much are you playing with that currently?
How much is your hope for the future of being able to analyze the content of the video itself?
Well, we have been working on that also since I came to YouTube.
Analyzing the content.
Analyzing the content of the video, right?
And what I can tell you is that our ability to do it well is still somewhat crude.
We can tell if it's a music video, we can tell if it's a sports video, we can probably
tell you that people are playing soccer.
We probably can't tell whether it's Manchester United or my daughter's soccer team.
So these things are kind of difficult and using them, we can use them in some ways.
So for instance, we use that kind of information to understand and inform these clusters that
I talked about.
And also maybe to add some words like soccer, for instance, to the video, if it doesn't
occur in the title or the description, which is remarkable that often it doesn't.
One of the things that I ask creators to do is please help us out with the title and the
description.
For instance, we were a few years ago having a live stream of some competition for World
of Warcraft on YouTube.
And it was a very important competition, but if you typed World of Warcraft in search,
you wouldn't find it.
World of Warcraft wasn't in the title?
World of Warcraft wasn't in the title.
It was match 478, you know, A team versus B team and World of Warcraft wasn't in the
title.
I'm just like, come on, give me.
Being literal on the internet is actually very uncool, which is the problem.
Oh, is that right?
Well, I mean, in some sense, well, some of the greatest videos, I mean, there's a humor
to just being indirect, being witty and so on.
And actually being, you know, machine learning algorithms want you to be, you know, literal,
right?
You just want to say what's in the thing, be very, very simple.
And in some sense that gets away from wit and humor.
So you have to play with both, right?
But you're saying that for now, sort of the content of the title, the content of the description,
the actual text is one of the best ways for the algorithm to find your video and put them
in the right cluster.
That's right.
And I would go further and say that if you want people, human beings to select your video
in search, then it helps to have, let's say World of Warcraft in the title.
Because why would a person, you know, if they're looking at a bunch, they type World of Warcraft
and they have a bunch of videos, all of whom say World of Warcraft, except the one that
you uploaded.
Well, even the person is going to think, well, maybe this isn't somehow search made a mistake.
This isn't really about World of Warcraft.
So it's important not just for the machine learning systems, but also for the people
who might be looking for this sort of thing.
They get a clue that it's what they're looking for by seeing that same thing prominently
in the title of the video.
Okay.
Let me push back on that.
So I think from the algorithm perspective, yes, but if they typed in World of Warcraft
and saw a video that with the title simply winning and the thumbnail has like a sad orc
or something, I don't know, right?
Like I think that's much, it gets your curiosity up.
And then if they could trust that the algorithm was smart enough to figure out somehow that
this is indeed a World of Warcraft video, that would have created the most beautiful
experience.
I think in terms of just the wit and the humor and the curiosity that we human beings naturally
have.
But you're saying, I mean, realistically speaking, it's really hard for the algorithm
to figure out that the content of that video will be a World of Warcraft video.
And you have to accept that some people are going to skip it.
Yeah.
Right?
I mean, and so you're right.
The people who don't skip it and select it are going to be delighted, but other people
might say, yeah, this is not what I was looking for.
And making stuff discoverable, I think is what you're really working on and hoping.
So yeah.
So from your perspective, put stuff in the title description.
And remember the collaborative filtering part of the system starts by the same user watching
videos together, right?
So the way that they're probably going to do that is by searching for them.
That's a fascinating aspect of it.
It's like ant colonies.
That's how they find stuff.
So I mean, what degree for collaborative filtering in general is one curious ant, one curious
user, essential?
So just a person who is more willing to click on random videos and sort of explore these
cluster spaces.
In your sense, how many people are just like watching the same thing over and over and
over and over?
And how many are just like the explorers and just kind of like click on stuff and then
help the other ant in the ant's colony discover the cool stuff?
Do you have a sense of that at all?
§04Transcript · 43:51–58:24
I really don't think I have a sense for the relative sizes of those groups.
But I would say that people come to YouTube with some certain amount of intent.
And as long as they, to the extent to which they try to satisfy that intent, that certainly
helps our systems, right?
Because our systems rely on kind of a faithful amount of behavior, right?
And there are people who try to trick us, right?
There are people and machines that try to associate videos together that really don't
belong together, but they're trying to get that association made because it's profitable
for them.
And so we have to always be resilient to that sort of attempt at gaming the systems.
So speaking to that, there's a lot of people that in a positive way, perhaps, I don't know,
I don't like it, but like to want to try to game the system to get more attention.
Everybody creators in a positive sense want to get attention, right?
So how do you work in this space when people create more and more sort of click baity titles
and thumbnails?
Sort of very to ask him, Derek has made a video where basically describes that it seems
what works is to create a high quality video, really good video, where people would want
to watch it once they click on it, but have click baity titles and thumbnails to get them
to click on it in the first place.
And he's saying, I'm embracing this fact, I'm just going to keep doing it.
And I hope you forgive me for doing it and you will enjoy my videos once you click on
them.
So in what sense do you see this kind of click bait style attempt to manipulate, to get people
in the door to manipulate the algorithm or play with the algorithm or game the algorithm?
I think that you can look at it as an attempt to game the algorithm.
But even if you were to take the algorithm out of it and just say, okay, well, all these
videos happen to be lined up, which the algorithm didn't make any decision about which one to
put at the top or the bottom, but they're all lined up there, which one are the people
going to choose?
And I'll tell you the same thing that I told Derek is, I have a bookshelf and they have
two kinds of books on them, science books.
I have my math books from when I was a student and they all look identical except for the
titles on the covers.
They're all yellow, they're all from Springer and they're every single one of them.
The cover is totally the same.
Yes.
Right?
Yeah.
On the other hand, I have other more pop science type books and they all have very interesting
covers and they have provocative titles and things like that.
I wouldn't say that they're click baity because they are indeed good books.
And I don't think that they cross any line, but that's just a decision you have to make.
Like the people who write classical recursion theory by Piero di Freddie, he was fine with
the yellow title and nothing more.
Whereas I think other people who wrote a more popular type book understand that they need
to have a compelling cover and a compelling title.
And I don't think there's anything really wrong with that.
We do take steps to make sure that there is a line that you don't cross.
And if you go too far, maybe your thumbnail is especially racy or it's all caps with too
many exclamation points, we observe that users are sometimes offended by that.
And so for the users who are offended by that, we will then depress or suppress those videos.
And which reminds me, there's also another signal where users can say, I don't know if
it was recently added, but I really enjoy it.
Just saying, something like, I don't want to see this video anymore or something like,
like this is a, like there's certain videos that just cut me the wrong way.
Like just, just jump out at me, it's like, I don't want to, I don't want this.
And it feels really good to clean that up, to be like, I don't, that's not, that's not
for me.
I don't know.
I think that might've been recently added, but that's also a really strong signal.
Yes, absolutely.
Right.
We don't want to make a recommendation that people are unhappy with.
And that makes me, that particular one makes me feel good as a user in general and as a
machine learning person.
Cause I feel like I'm helping the algorithm.
My interactions on YouTube don't always feel like I'm helping the algorithm.
Like I'm not reminded of that fact.
Like for example, Tesla and Autopilot and Elon Musk create a feeling for their customers,
for people that own Teslas, that they're helping the algorithm of Tesla vehicles.
Like they're all, like are really proud they're helping the fleet learn.
I think YouTube doesn't always remind people that you're helping the algorithm get smarter.
And for me, I love that idea.
Like we're all collaboratively, like Wikipedia gives that sense that we're all together creating
a beautiful thing.
YouTube is a, doesn't always remind me of that.
It's a, this conversation is reminding me of that, but.
Well that's a good tip.
We should keep that fact in mind when we design these features.
I'm not sure I really thought about it that way, but that's a very interesting perspective.
It's an interesting question of personalization that I feel like when I click like on a video,
I'm just improving my experience.
It would be great.
It would make me personally, people are different, but make me feel great if I was helping also
the YouTube algorithm broadly say something.
You know what I'm saying?
Like there's a, that I don't know if that's human nature, but you want the products you
love, and I certainly love YouTube, like you want to help it get smarter, smarter, smarter
because there's some kind of coupling between our lives together being better.
If YouTube is better than I will, my life will be better.
And there's that kind of reasoning.
I'm not sure what that is and I'm not sure how many people share that feeling.
That could be just a machine learning feeling.
But on that point, how much personalization is there in terms of next video recommendations?
So is it kind of all really boiling down to clustering?
Like if I'm the nearest clusters to me and so on and that kind of thing, or how much
is personalized to me, the individual completely?
It's very, very personalized.
So your experience will be quite a bit different from anybody else's who's watching that same
video, at least when they're logged in.
And the reason is that we found that users often want two different kinds of things when
they're watching a video.
Sometimes they want to keep watching more on that topic or more in that genre.
And other times they just are done and they're ready to move on to something else.
And so the question is, well, what is the something else?
And one of the first things one can imagine is, well, maybe something else is the latest
video from some channel to which you've subscribed.
And that's going to be very different for you than it is for me.
And even if it's not something that you subscribe to, it's something that you watch a lot.
And again, that'll be very different on a person by person basis.
And so even the Watch Next, as well as the homepage, of course, is quite personalized.
So what, we mentioned some of the signals, but what does success look like?
What does success look like in terms of the algorithm creating a great long term experience
for a user?
Or to put another way, if you look at the videos I've watched this month, how do you
know the algorithm succeeded for me?
I think, first of all, if you come back and watch more YouTube, then that's one indication
that you found some value from it.
So just the number of hours is a powerful indicator.
Well, I mean, not the hours themselves, but the fact that you return on another day.
So that's probably the most simple indicator.
People don't come back to things that they don't find value in, right?
There's a lot of other things that they could do.
But like I said, ideally, we would like everybody to feel that YouTube enriches their lives
and that every video they watched is the best one they've ever watched since they've started
watching YouTube.
And so that's why we survey them and ask them, is this one to five stars?
And so our version of success is every time someone takes that survey, they say it's five
stars.
And if we ask them, is this the best video you've ever seen on YouTube?
They say, yes, every single time.
So it's hard to imagine that we would actually achieve that.
Maybe asymptotically we would get there, but that would be what we think success is.
It's funny.
I've recently said somewhere, I don't know, maybe tweeted, but that Ray Dalio has this
video on the economic machine, I forget what it's called, but it's a 30 minute video.
And I said it's the greatest video I've ever watched on YouTube.
It's like I watched the whole thing and my mind was blown as a very crisp, clean description
of how the, at least the American economic system works.
It's a beautiful video.
And I was just, I wanted to click on something to say this is the best thing.
This is the best thing ever.
Please let me, I can't believe I discovered it.
I mean, the views and the likes reflect its quality, but I was almost upset that I haven't
found it earlier and wanted to find other things like it.
I don't think I've ever felt that this is the best video I've ever watched.
That was that.
And to me, the ultimate utopia, the best experiences were every single video.
Where I don't see any of the videos I regret and every single video I watch is one that
actually helps me grow, helps me enjoy life, be happy and so on.
So that's a heck of a, that's one of the most beautiful and ambitious, I think, machine
learning tasks.
So when you look at a society as opposed to the individual user, do you think of how YouTube
is changing society when you have these millions of people watching videos, growing, learning,
changing, having debates?
Do you have a sense of, yeah, what the big impact on society is?
I think it's huge, but do you have a sense of what direction we're taking this world?
Well, I mean, I think openness has had an impact on society already.
There's a lot of...
What do you mean by openness?
Well, the fact that unlike other mediums, there's not someone sitting at YouTube who
decides before you can upload your video, whether it's worth having you upload it or
worth anybody seeing it really, right?
And so there are some creators who say, like, I wouldn't have this opportunity to reach
an audience.
Tyler Oakley often said that he wouldn't have had this opportunity to reach this audience
if it weren't for YouTube.
And so I think that's one way in which YouTube has changed society.
I know that there are people that I work with from outside the United States, especially
from places where literacy is low, and they think that YouTube can help in those places
because you don't need to be able to read and write in order to learn something important
for your life, maybe how to do some job or how to fix something.
And so that's another way in which I think YouTube is possibly changing society.
So I've worked at YouTube for eight, almost nine years now.
And it's fun because I meet people and you tell them where you work, you say you work
on YouTube and they immediately say, I love YouTube, right?
Which is great, makes me feel great.
But then of course, when I ask them, well, what is it that you love about YouTube?
Not one time ever has anybody said that the search works outstanding or that the recommendations
are great.
What they always say when I ask them, what do you love about YouTube is they immediately
start talking about some channel or some creator or some topic or some community that they
found on YouTube and that they just love.
And so that has made me realize that YouTube is really about the video and connecting the
people with the videos.
And then everything else kind of gets out of the way.
So beyond the video, it's an interesting, because you kind of mentioned creator.
What about the connection with just the individual creators as opposed to just individual video?
So like I gave the example of Ray Dalio video that the video itself is incredible, but there's
some people who are just creators that I love.
One of the cool things about people who call themselves YouTubers or whatever is they have
a journey.
They usually, almost all of them, they suck horribly in the beginning and then they kind
of grow and then there's that genuineness in their growth.
So YouTube clearly wants to help creators connect with their audience in this kind of
way.
So how do you think about that process of helping creators grow, helping them connect
with their audience, develop not just individual videos, but the entirety of a creator's life
on YouTube?
Well, I mean, we're trying to help creators find the biggest audience that they can find.
§05Transcript · 58:24–1:12:14
And the reason why that's, you brought up creator versus video, the reason why creator
channel is so important is because if we have a hope of people coming back to YouTube, well,
they have to have in their minds some sense of what they're going to find when they come
back to YouTube.
If YouTube were just the next viral video and I have no concept of what the next viral
video could be, one time it's a cat playing a piano and the next day it's some children
interrupting a reporter and the next day it's some other thing happening, then it's hard
for me to, when I'm not watching YouTube, say, gosh, I really would like to see something
from someone or about something, right?
And so that's why I think this connection between fans and creators is so important
for both, because it's a way of sort of fostering a relationship that can play out into the
future.
Let me talk about kind of a dark and interesting question in general, and again, a topic that
you or nobody has an answer to.
But social media has a sense of, it gives us highs and it gives us lows in the sense
that sort of creators often speak about having sort of burnout and having psychological ups
and downs and challenges mentally in terms of continuing the creation process.
There's a momentum, there's a huge excited audience that makes creators feel great.
And I think it's more than just financial.
I think it's literally just, they love that sense of community.
It's part of the reason I upload to YouTube.
I don't care about money, never will.
What I care about is the community, but some people feel like this momentum, and even when
there's times in their life when they don't feel, you know, for some reason don't feel
like creating.
So how do you think about burnout, this mental exhaustion that some YouTube creators go through?
Is that something we have an answer for?
Is that something, how do we even think about that?
Well, the first thing is we want to make sure that the YouTube systems are not contributing
to this sense, right?
And so we've done a fair amount of research to demonstrate that you can absolutely take
a break.
If you are a creator and you've been uploading a lot, we have just as many examples of people
who took a break and came back more popular than they were before as we have examples
of going the other way.
Yeah.
Can we pause on that for a second?
So the feeling that people have, I think, is if I take a break, everybody, the party
will leave, right?
So if you could just linger on that.
So in your sense that taking a break is okay.
Yes, taking a break is absolutely okay.
And the reason I say that is because we have, we can observe many examples of being, of
creators coming back very strong and even stronger after they have taken some sort of
break.
And so I just want to dispel the myth that this somehow necessarily means that your channel
is going to go down or lose views.
That is not the case.
We know for sure that this is not a necessary outcome.
And so we want to encourage people to make sure that they take care of themselves.
That is job one, right?
You have to look after yourself and your mental health.
And I think that it probably, in some of these cases, contributes to better videos once they
come back, right?
Because a lot of people, I mean, I know myself, if I burn out on something, then I'm probably
not doing my best work, even though I can keep working until I pass out.
And so I think that the taking a break may even improve the creative ideas that someone
has.
Okay.
I think that's a really important thing to sort of dispel.
I think that applies to all of social media, like literally I've taken a break for a day
every once in a while.
Sorry.
Sorry if that sounds like a short time, but even like, sorry, email, just taking a break
from email, or only checking email once a day, especially when you're going through
something psychologically in your personal life or so on, or really not sleeping much
because of work deadlines, it can refresh you in a way that's profound.
And so the same applies.
It was there when you came back, right?
It's there.
And it looks different, actually, when you come back.
You're sort of brighter eyed with some coffee, everything, the world looks better.
So it's important to take a break when you need it.
So you've mentioned kind of the YouTube algorithm that isn't E equals MC squared, it's not the
single equation, it's potentially sort of more than a million lines of code.
Is it more akin to what successful autonomous vehicles today are, which is they're just
basically patches on top of patches of heuristics and human experts really tuning the algorithm
and have some machine learning modules?
Or is it becoming more and more a giant machine learning system with humans just doing a little
bit of tweaking here and there?
What's your sense?
First of all, do you even have a sense of what is the YouTube algorithm at this point?
And however much you do have a sense, what does it look like?
Well, we don't usually think about it as the algorithm because it's a bunch of systems
that work on different services.
The other thing that I think people don't understand is that what you might refer to
as the YouTube algorithm from outside of YouTube is actually a bunch of code and machine learning
systems and heuristics, but that's married with the behavior of all the people who come
to YouTube every day.
So the people part of the code, essentially.
Exactly.
If there were no people who came to YouTube tomorrow, then the algorithm wouldn't work
anymore.
Right.
That's the whole part of the algorithm.
And so when people talk about, well, the algorithm does this, the algorithm does that, it's sometimes
hard to understand, well, it could be the viewers are doing that.
And the algorithm is mostly just keeping track of what the viewers do and then reacting to
those things in sort of more fine grain situations.
And I think that this is the way that the recommendation system and the search system
and probably many machine learning systems evolve is you start trying to solve a problem
and the first way to solve a problem is often with a simple heuristic.
And you want to say, what are the videos we're going to recommend?
Well, how about the most popular ones?
That's where you start.
And over time, you collect some data and you refine your situation so that you're making
less heuristics and you're building a system that can actually learn what to do in different
situations based on some observations of those situations in the past.
And you keep chipping away at these heuristics over time.
And so I think that just like with diversity, I think the first diversity measure we took
was, okay, not more than three videos in a row from the same channel.
It's a pretty simple heuristic to encourage diversity, but it worked, right?
Who needs to see four, five, six videos in a row from the same channel?
And over time, we try to chip away at that and make it more fine grain and basically
have it remove the heuristics in favor of something that can react to individuals and
individual situations.
So how do you, you mentioned, you know, we know that something worked.
How do you get a sense when decisions are kind of A, B testing that this idea was a
good one, this was not so good?
How do you measure that and across which time scale, across how many users, that kind of
thing?
Well, you mentioned the A, B experiments.
And so just about every single change we make to YouTube, we do it only after we've run
a A, B experiment.
And so in those experiments, which run from one week to months, we measure hundreds, literally
hundreds of different variables and measure changes with confidence intervals in all of
them, because we really are trying to get a sense for ultimately, does this improve
the experience for viewers?
That's the question we're trying to answer.
And an experiment is one way because we can see certain things go up and down.
So for instance, if we noticed in the experiment, people are dismissing videos less frequently,
or they're saying that they're more satisfied, they're giving more videos five stars after
they watch them, then those would be indications that the experiment is successful, that it's
improving the situation for viewers.
But we can also look at other things, like we might do user studies, where we invite
some people in and ask them, like, what do you think about this?
What do you think about that?
How do you feel about this?
And other various kinds of user research.
But ultimately, before we launch something, we're going to want to run an experiment.
So we get a sense for what the impact is going to be, not just to the viewers, but also to
the different channels and all of that.
An absurd question.
Nobody knows.
Well, actually, it's interesting.
Maybe there's an answer.
But if I want to make a viral video, how do I do it?
I don't know how you make a viral video.
I know that we have in the past tried to figure out if we could detect when a video was going
to go viral.
And those were, you take the first and second derivatives of the view count and maybe use
that to do some prediction.
But I can't say we ever got very good at that.
Oftentimes we look at where the traffic was coming from.
If a lot of the viewership is coming from something like Twitter, then maybe it has
a higher chance of becoming viral than if it were coming from search or something.
But that was just trying to detect a video that might be viral.
How to make one, I have no idea.
You get your kids to interrupt you while you're on the news or something.
Absolutely.
But after the fact, on one individual video, sort of ahead of time predicting is a really
hard task.
But after the video went viral, in analysis, can you sometimes understand why it went viral?
From the perspective of YouTube broadly, first of all, is it even interesting for YouTube
that a particular video is viral or does that not matter for the individual, for the experience
of people?
Well, I think people expect that if a video is going viral and it's something they would
be interested in, then I think they would expect YouTube to recommend it to them.
Right.
So if something's going viral, it's good to just let the wave, let people ride the wave
of its violence.
Well, I mean, we want to meet people's expectations in that way, of course.
So like I mentioned, I hung out with Derek Mueller a while ago, a couple of months back.
He's actually the person who suggested I talk to you on this podcast.
All right.
Well, thank you, Derek.
At that time, he just recently posted an awesome science video titled, why are 96 million black
balls on this reservoir?
And in a matter of, I don't know how long, but like a few days, he got 38 million views
and it's still growing.
Is this something you can analyze and understand why it happened, this video and you want a
particular video like it?
I mean, we can surely see where it was recommended, where it was found, who watched it and those
sorts of things.
So it's actually, sorry to interrupt, it is the video which helped me discover who Derek
is.
I didn't know who he is before.
So I remember, you know, usually I just have all of these technical, boring MIT Stanford
talks in my recommendation because that's how I watch.
And then all of a sudden there's this black balls and reservoir video with like an excited
nerd with like just, why is this being recommended to me?
So I clicked on it and watched the whole thing and it was awesome.
And then a lot of people had that experience, like why was I recommended this?
But they all of course watched it and enjoyed it, which is, what's your sense of this just
wave of recommendation that comes with this viral video that ultimately people get enjoy
after they click on it?
Well, I think it's the system, you know, basically doing what anybody who's recommending something
would do, which is you show it to some people and if they like it, you say, okay, well,
can I find some more people who are a little bit like them?
Okay, I'm going to try it with them.
§06Transcript · 1:12:14–1:26:21
Oh, they like it too.
Let me expand the circle some more, find some more people.
Oh, it turns out they like it too.
And you just keep going until you get some feedback that says that, no, now you've gone
too far.
These people don't like it anymore.
And so I think that's basically what happened.
And you asked me about how to make a video go viral or make a viral video.
I don't think that if you or I decided to make a video about 96 million balls that it
would also go viral.
It's possible that Derek made like the canonical video about those black balls in the lake.
He did actually.
Right.
And I don't know whether or not just following along is the secret.
Yeah.
But it's fascinating.
I mean, just like you said, the algorithm sort of expanding that circle and then figuring
out that more and more people did enjoy it and that sort of phase shift of just a huge
number of people enjoying it and the algorithm quickly, automatically, I assume, figuring
that out.
I don't know, the dynamics of psychology of that is a beautiful thing.
So what do you think about the idea of clipping?
Too many people annoyed me into doing it, which is they were requesting it.
They said it would be very beneficial to add clips in like the coolest points and actually
have explicit videos.
Like I'm re uploading a video, like a short clip, which is what the podcasts are doing.
Do you see as opposed to, like I also add timestamps for the topics, do you want the
clip?
Do you see YouTube somehow helping creators with that process or helping connect clips
to the original videos or is that just on a long list of amazing features to work towards?
Yeah.
I mean, it's not something that I think we've done yet, but I can tell you that I think
clipping is great and I think it's actually great for you as a creator.
And here's the reason.
If you think about, I mean, let's say the NBA is uploading videos of its games.
Well, people might search for warriors versus rockets or they might search for Steph Curry.
And so a highlight from the game in which Steph Curry makes an amazing shot is an opportunity
for someone to find a portion of that video.
And so I think that you never know how people are going to search for something that you've
created.
And so you want to, I would say you want to make clips and add titles and things like
that so that they can find it as easily as possible.
Do you have a dream of a future, perhaps a distant future when the YouTube algorithm
figures that out?
Sort of automatically detects the parts of the video that are really interesting, exciting,
potentially exciting for people and sort of clip them out in this incredibly rich space.
Cause if you talk about, if you talk, even just this conversation, we probably covered
30, 40 little topics and there's a huge space of users that would find, you know, 30% of
those topics really interesting.
And that space is very different.
It's something that's beyond my ability to clip out, right?
But the algorithm might be able to figure all that out, sort of expand into clips.
Do you have a, do you think about this kind of thing?
Do you have a hope or dream that one day the algorithm will be able to do that kind of
deep content analysis?
Well, we've actually had projects that attempt to achieve this, but it really does depend
on understanding the video well and our understanding of the video right now is quite crude.
And so I think it would be especially hard to do it with a conversation like this.
One might be able to do it with, let's say a soccer match more easily, right?
You could probably find out where the goals were scored.
And then of course you, you need to figure out who it was that scored the goal and, and
that might require a human to do some annotation.
But I think that trying to identify coherent topics in a transcript, like, like the one
of our conversation is, is not something that we're going to be very good at right away.
And I was speaking more to the general problem actually of being able to do both a soccer
match and our conversation without explicit sort of almost my, my hope was that there
exists an algorithm that's able to find exciting things in video.
So Google now on Google search will help you find the segment of the video that you're
interested in.
So if you search for something like how to change the filter in my dishwasher, then if
there's a long video about your dishwasher and this is the part where the person shows
you how to change the filter, then, then it will highlight that area.
And provide a link directly to it.
And do you know if, from your recollection, do you know if the thumbnail reflects, like,
what's the difference between showing the full video and the shorter clip?
Do you know how it's presented in search results?
I don't remember how it's presented.
And the other thing I would say is that right now it's based on creator annotations.
Ah, got it.
So it's not the thing we're talking about.
But folks are working on the more automatic version.
It's interesting, people might not imagine this, but a lot of our systems start by using
almost entirely the audience behavior.
And then as they get better, the refinement comes from using the content.
And I wish, I know there's privacy concerns, but I wish YouTube explored the space, which
is sort of putting a camera on the users if they allowed it, right, to study their, like,
I did a lot of emotion recognition work and so on, to study actual sort of richer signal.
One of the cool things when you upload 360 like VR video to YouTube, and I've done this
a few times, so I've uploaded myself, it's a horrible idea.
Some people enjoyed it, but whatever.
The video of me giving a lecture in 360 with a 360 camera, and it's cool because YouTube
allows you to then watch where did people look at?
There's a heat map of where, you know, of where the center of the VR experience was.
And it's interesting because that reveals to you, like, what people looked at.
It's not always what you were expecting.
In the case of the lecture, it's pretty boring, it is what we were expecting, but we did a
few funny videos where there's a bunch of people doing things, and everybody tracks
those people.
You know, in the beginning, they all look at the main person and they start spreading
around and looking at the other people.
It's fascinating.
So that kind of, that's a really strong signal of what people found exciting in the video.
I don't know how you get that from people just watching, except they tuned out at this
point.
Like, it's hard to measure this moment was super exciting for people.
I don't know how you get that signal.
Maybe comment, is there a way to get that signal where this was like, this is when their
eyes opened up and they're like, like for me with the Ray Dalio video, right?
Like at first I was like, okay, this is another one of these like dumb it down for you videos.
And then you like start watching, it's like, okay, there's really crisp, clean, deep explanation
of how the economy works.
That's where I like set up and started watching, right?
That moment, is there a way to detect that moment?
The only way I can think of is by asking people to label it.
You mentioned that we're quite far away in terms of doing video analysis, deep video
analysis.
Of course, Google, YouTube, you know, we're quite far away from solving autonomous driving
problem too.
So it's a...
I don't know.
I think we're closer to that.
Well, the, you know, you never know.
And the Wright brothers thought they're never, they're not going to fly for 50 years, three
years before they flew.
So what are the biggest challenges would you say?
Is it the broad challenge of understanding video, understanding natural language, understanding
the challenge before the entire machine learning community or just being able to understand
data?
Is there something specific to video that's even more challenging than understanding natural
language understanding?
What's your sense of what the biggest challenge is?
Video is just so much information.
And so precision becomes a real problem.
It's like, you know, you're trying to classify something and you've got a million classes
and the distinctions among them, at least from a machine learning perspective are often
pretty small, right?
Like, you know, you need to see this person's number in order to know which player it is.
And there's a lot of players or you need to see, you know, the logo on their chest in
order to know like which team they play for.
And so, and that's just figuring out who's who, right?
And then you go further and saying, okay, well, you know, was that a goal?
Was it not a goal?
Like, is that an interesting moment as you said, or is that not an interesting moment?
These things can be pretty hard.
So okay.
So Yann LeCun, I'm not sure if you're familiar sort of with his current thinking and work.
So he believes that self, what he's referring to as self supervised learning will be the
solution sort of to achieving this kind of greater level of intelligence.
In fact, the thing he's focusing on is watching video and predicting the next frame.
So predicting the future of video, right?
So for now we're very far from that, but his thought is because it's unsupervised or as
he refers to as self supervised, you know, if you watch enough video, essentially if
you watch YouTube, you'll be able to learn about the nature of reality, the physics,
the common sense reasoning required by just teaching a system to predict the next frame.
So he's confident this is the way to go.
So for you, from the perspective of just working with this video, how do you think an algorithm
that just watches all of YouTube, stays up all day and night watching YouTube would be
able to understand enough of the physics of the world about the way this world works,
be able to do common sense reasoning and so on?
Well, I mean, we have systems that already watch all the videos on YouTube, right?
But they're just looking for very specific things, right?
They're supervised learning systems that are trying to identify something or classify something.
And I don't know if, I don't know if predicting the next frame is really going to get there
because I'm not an expert on compression algorithms, but I understand that that's kind of what
compression video compression algorithms do is they basically try to predict the next
frame and then fix up the places where they got it wrong.
And that leads to higher compression than if you actually put all the bits for the next
frame there.
So I don't know if I believe that just being able to predict the next frame is going to
be enough because there's so many frames and even a tiny bit of error on a per frame basis
can lead to wildly different videos.
So the thing is, the idea of compression is one way to do compression is to describe through
text what's contained in the video.
That's the ultimate high level of compression.
So the idea is traditionally when you think of video image compression, you're trying
to maintain the same visual quality while reducing the size.
But if you think of deep learning from a bigger perspective of what compression is, is you're
trying to summarize the video.
And the idea there is if you have a big enough neural network, just by watching the next,
trying to predict the next frame, you'll be able to form a compression of actually understanding
what's going on in the scene.
If there's two people talking, you can just reduce that entire video into the fact that
two people are talking and maybe the content of what they're saying and so on.
That's kind of the open ended dream.
So I just wanted to sort of express that because it's interesting, compelling notion, but it
is nevertheless true that video, our world is a lot more complicated than we get a credit
for.
I mean, in terms of search and discovery, we have been working on trying to summarize
videos in text or with some kind of labels for eight years at least.
And you know, and we're kind of so, so.
So if you were to say the problem is a hundred percent solved and eight years ago was zero
percent solved, where are we on that timeline would you say?
Yeah.
To summarize a video well, maybe less than a quarter of the way.
So on that topic, what does YouTube look like 10, 20, 30 years from now?
I mean, I think that YouTube is evolving to take the place of TV.
I grew up as a kid in the seventies and I watched a tremendous amount of television
and I feel sorry for my poor mom because people told her at the time that it was going to
rot my brain and that she should kill her television.
But anyway, I mean, I think that YouTube is at least for my family, a better version of
§07Transcript · 1:26:21–1:30:57
television, right?
It's one that is on demand.
It's more tailored to the things that my kids want to watch.
And also they can find things that they would never have found on television.
And so I think that at least from just observing my own family, that's where we're headed is
that people watch YouTube kind of in the same way that I watched television when I was younger.
So from a search and discovery perspective, what do you, what are you excited about in
the five, 10, 20, 30 years?
Like what kind of things?
It's already really good.
I think it's achieved a lot of, of course we don't know what's possible.
So it's the task of search of typing in the text or discovering new videos by the next
recommendation.
So I personally am really happy with the experience.
I continuously, I rarely watch a video that's not awesome from my own perspective, but what's,
what else is possible?
What are you excited about?
Well, I think introducing people to more of what's available on YouTube is not only very
important to YouTube and to creators, but I think it will help enrich people's lives
because there's a lot that I'm still finding out is available on YouTube that I didn't
even know.
I've been working YouTube eight years and it wasn't until last year that I learned that,
that I could watch USC football games from the 1970s.
Like I didn't even know that was possible until last year and I've been working here
quite some time.
So, you know, what was broken about, about that?
That it took me seven years to learn that this stuff was already on YouTube even when
I got here.
So I think there's a big opportunity there.
And then as I said before, you know, we want to make sure that YouTube finds a way to ensure
that it's acting responsibly with respect to society and enriching people's lives.
So we want to take all of the great things that it does and make sure that we are eliminating
the negative consequences that might happen.
And then lastly, if we could get to a point where all the videos people watch are the
best ones they've ever watched, that'd be outstanding too.
Do you see in many senses becoming a window into the world for people?
It's especially with live video, you get to watch events.
I mean, it's really, it's the way you experience a lot of the world that's out there is better
than TV in many, many ways.
So do you see becoming more than just video?
Do you see creators creating visual experiences and virtual worlds that if I'm, I'm talking
crazy now, but sort of virtual reality and entering that space, or is that at least for
now totally outside what YouTube is thinking about?
I mean, I think Google is thinking about virtual reality.
I don't think about virtual reality too much.
I know that we would want to make sure that YouTube is there when virtual reality becomes
something or if virtual reality becomes something that a lot of people are interested in.
But I haven't seen it really take off yet.
Take off.
Well, the future is wide open.
Christos, I've been really looking forward to this conversation.
It's been a huge honor.
Thank you for answering some of the more difficult questions I've asked.
I'm really excited about what YouTube has in store for us.
It's one of the greatest products I've ever used and continues.
So thank you so much for talking to me.
It's my pleasure.
Thanks for asking me.
Thanks for listening to this conversation.
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And now, let me leave you with some words of wisdom from Marcel Proust.
The real voyage of discovery consists not in seeking new landscapes, but in having new
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Thank you for listening and hope to see you next time.