How YouTube Works - Computerphile

How does YouTube work and why do videos buffer? See more in the full description.

Our thanks to the staff at YouTube for giving us their time.

Video by Sean Riley and Brady Haran.

NOTE ONE: This was filmed at YouTube HQ in San Bruno. It was filmed before the much-discussed changes were made to YouTube comments section - we have not asked questions about that.

NOTE TWO: This is a Computerphile video - it was NOT made by YouTube or reflect the company's official views. Staff were kind enough to answer some of our questions (well, most of them), but they did not edit the video or "approve" it - any mistakes in the editing or animations are most likely our own.

NOTE THREE: A video about the YouTube algorithm (how videos are recommended) is coming soon to Computerphile - so you really should subscribe.

NOTE FOUR: The snowboarder is Sean!

NOTE FIVE: Music on snowboarding film courtesy Hudson Super Six

NOTE SIX: Error on the graphics where it says 320p - actually should read 360p

[kipkay]

I love how Youtube partners need to find out technical issues by stumbling upon a video...not by any type of support.

[WtbgoldBlogspot]

I love the sense of personal and corporate responsibility the YouTube employees are showing here, especially when they say things like "I think they do blame me for YouTube performance issues, but I think they're correct." Saying that with a smile, was intriguing and made me appreciate the company more than anything else in the video.

[irvin]

I do see that these improvements have benefited me before it'd take forever to load up a simple 3 minute video, now it plays seamlessly.

[Computerphile]

For more information about this video, please see the full video description... and before you ask, it was filmed BEFORE the changes to the comments section, so we have not asked about that... (although a film on the YouTube Algorithm is coming soon)

[michaeljreedy]

Can we all just take a second to appreciate the guy that edits the computerphile videos? There's some nice editing in there.

[pa]

I've been having a YouTube evening and this is the only video that didn't buffer while I was watching it. Wow.

[ITR]

I usually don't care about buffering that much, I just pause the video. What really annoys me is that the video glitches up if I pause while it's buffering, or just randomly stops loading the video from YouTube so I have to reload the page :(

[HiAdrian]

For me once I get the spinning icon, the video is basically dead. It never recovers and I have to refresh the page and start over. I have a 50mbit/s connection, but YouTube has been awful for many months now. I suspect they just saved on distribution infrastructure in non-US locations.

I tried the "block local ISP mirror" method, but it didn't make any difference.

[eduardog]

You know what would be great? If they removed DASH playback, thus allowing us to pause a video, let it load all the way through, then watch the whole thing with no spinning circle.

[EddieKMusic]

at 5:44 there's an error in the video. It says 320p instead of 360p.

[mittfh]

Regarding some comments below about if it's possible to buffer the entire video before playback starts, I've always found that if you play even a couple of second's worth then pause, it buffers the rest (as seen by the expanding light grey line in the timeline / progress bar). In addition, there have historically always been numerous browser extensions which will auto-pause the video, so allowing it to completely buffer before you manually unpause it. Several also allow you to set a default quality and/or auto-expand the video window (one called Magic Actions will do the lot - and more besides - available for both Chrome and FireFox).

[steevf]

I haven't seen the spinner ever appear in the last year or so, but the video will still just stop and quite often will never continue.  I watch my network traffic when  video is playing and I can see how it will just send it in chunks but then suddenly it just stops sending anything.  Video stops, I never see a spinner and the only way I can get it to start up again is move the slider.  Sometimes I'll be watching a video at 480p, it will stop and grey out(disable) that option.  I select 720p and it continues.  I have enough bandwidth to stream 1080p videos but I never use it because it always stops after the first 10 seconds or so and never recovers.    I can steam full HD Netflix and it never stops.  But Youtube, just seems to never get through all the time.  I do wonder how much my ISP is involved screwing this up.

[rich]

Yes, the youtube videos are great all things considered. I would love to hear about how they keep screwing up everything else on the site more and more with every update tho.

[randomweeaboo]

What makes me mad is that videos won't fully buffer, they only go a minute or two out. Which seems inefficient to me.

Where's the YouTube option that lets me automatically stream in HD? There's a box that says "Always play highest quality" or whatever, but as far as I can tell, 420p is clearly not the highest quality video.

Another issue I always had, especially on slower connections, was that you couldn't load the whole video before playback. It used to be you could pause it and the rest of the video would load, and then you could play the whole thing without worrying about buffering. Now, I pause it... and it loads about 20 seconds further... and then stops loading the video. So now I have to watch it all the way until it starts buffering again, then I can pause, wait for 20 more seconds, etc.

[TechLaboratories]

I wish other companies streaming video paid as much attention to the user experience of the video as YouTube does!

[ultravidz]

Honestly, what a great video.
I think a lot more people will discover computerfile with this one

[TechyBen]

"Your welcome to make choices, but you shouldn't have to".
TechyBen, choosing the res/bandwidth and making choices since 1980s! Thank you, don't change that.

[Cyphlix]

jraphics interchange format *eye twitches. Pronunciation aside - great video! 

[mexicanreformist]

This was such a incredibly fascinating video in the way we manage videos, and how we display them. The way we decide to retrieve our videos also has an effect to the quality it is presented. Whether it's your ISP or the lack of cache we need to really continue to innovate the way we transfer files.