To stream everywhere, Netflix encodes each movie 120 times | Hacker News Reader

To stream everywhere, Netflix encodes each movie 120 times

gigaom.com

43 pointstimf37 comments

A friend of mine, Baptiste Coudurier, is the person at Hulu who manages the transcoding of all their videos. He told me they also transcode a video to multiple versions to accommodate different streaming devices and bandwidth characteristics.

I think it only makes sense to lazily-transcode videos on demand (and cache them) when you have millions of videos (eg. Youtube). Netflix and Hulu have much smaller catalogs, so they can afford to transcode ahead of time, and it simplifies their processes.

I wonder if there's some lengthy preprocessing step that's common to transcoding regardless of the target resolution/quality. That way you could precompute and store the intermediary format and finish of the encoding to an arbitrary format as required.

For two-pass encoding, the video is first scanned to assess complexity, so a second encode pass can work out which frames require a higher bitrate to get the same quality. However this is not used that often, in favour of a quantiser approach, which uses a number to indicate target quality. The encoder then changes the bitrate depending on the frames complexity and the target quality/quantiser. The quantiser approach is much more common because it's easier to specify an output quality that is independent of resolution.

As for the actual encoding, nearly all the computation is very specific to the output resolution/quality. Luckily encoding multiple videos can be spread over many machines, and encoders can take advantage of multiple cores.

If this is true, then this should immediately put to rest the explanation (that I'll admit I bought into) that only one video format will win out (H.264 vs Ogg Theora/VP8 is the major discussion point) - as video streaming companies would be unwilling to re-encode their content for more than one format.

Apparently they are quite comfortable encoding as many as 120 instantiations of their videos.

Netflix has a limited catalog... YouTube has a much larger one by many orders of magnitude.

However they could still lazily trans code on demand (and cache the result).

>Netflix has a limited catalog... YouTube has a much larger one by many orders of magnitude.

Youtube offer their videos in vp8 along with h264.

Storage is cheap. Edge connections are not. It makes sense to have 120 instantiations of the videos if that huge multitude is necessary to optimally serve the plethora of mobile devices out there: you don't want to be negotiating for the worst bitrate out of a 720p encode if the device you're delivering too is only capable of 480x320 and can only gain access to 3G networks.

In fact, it is not unheard of for us to re-encode the entire catalog when a new, better format or codec comes along, or we add support for a new device.

Huh. You guys must have quite the rendering farm for that, eh?

EC2. 1000s of instances. :)

Spot pricing I hope! =)

> Apparently they are quite comfortable encoding as many as 120 instantiations of their videos.

There is more to it than just the number of videos (or storage requirements). You can get dedicated hardware h264 encoders easily (and relatively cheaply), not to mention the decoders in mobile devices. There's also quality to consider, effective quality per MB (important when targeting mobile devices), and all the things that fall into that (motion handling, prediction, etc).

I don't claim to be an expert, but from what I've read Ogg & WebM are fighting an uphill battle on the technical side of things. Part of this is no doubt due to h264 patents, but it's a shame the free solution isn't also the technically superior one.

Using sometimes 1000's of EC2 instances (for a bunch of movies, not just one).

this being an ideal application of simd kind of parallelism, i am wondering of a farm of gpu's might be much cheaper (and faster) rather than a general purpose cpu ?

AWS has farms of GPUs you can rent by the hour - http://aws.amazon.com/ec2/instance-types/ - Look at "Cluster GPU Instances"

digeek is right -- they have GPU instances too.

We don't actually use the GPU instances yet, but I think I heard we're moving over to them (need to check on that).

The article "The wretched state of GPU transcoding" disagrees: http://www.extremetech.com/computing/128681-the-wretched-sta...

At the end of the post there's this quote:

> Simply put, content owners who can deliver quickly and without error are getting more licensing revenue from Netflix.

Really? Can Netflix afford to be picky with content owners? It seems their main problem is the limited size of their online catalog...? They should take anything they can get!

I just finished watching "Elite Squad 2"; it's such a great movie (really, it is: see http://www.imdb.com/title/tt1555149/) that I wanted to watch the first one, but it's "only available on DVD".

Why, why, why?

Exactly. When The Pirate Bay has an infinite catalog, they can't afford to be picky.

The Pirate Bay doesn't have everything, but yes, it helps... ;-)

Because it's a way to upsell you.

That's not correct. It's because licensing movies on DVD is monumentally cheaper than licensing content for online streaming. One requires a deal with the studio, the other just requires picking up a DVD somewhere (see http://en.wikipedia.org/wiki/First-sale_doctrine).

The studio is upselling you - not the middleman - because you'll have to go out somewhere else and spend more money to buy the first version.

I think you misinterpreted.

We have $X to spend. We have $Y left at the end of the year ($Y < $X). We go though our system and say "who can deliver us the quickest, most error free, content? Ok, give them $Y for whatever they have that our customers might enjoy.

The reason you only see Elite Squad 2 is the same reason that you only see a lot of stuff -- because the price they wanted for the other one was too much.

Thanks for the clarification.

(I'm not sure that the technical quality of transmitted files is the best criterium to select content, though, even when it's the end of the year and we're talking about "leftover money").

Really? Can Netflix afford to be picky with content owners? It seems their main problem is the limited size of their online catalog...? They should take anything they can get!

Let me put it to you this way: If it ain't on Netflix, I ain't watching it. Now, I don't consider myself typical; usually I'm willing to do research, dig into things, I know multiple ways to "access" content, etc, etc. But at the end of the day, I'm tired (and lazy), and when it comes down to it, I'm browsing Netflix, which is full of stuff, so I almost never notice if something is missing. In this respect, I'm willing to bet I'm typical.

Content owners: either get on the bandwagon (and that means distributing to everyone, not just Netflix, who doesn't require exclusive deals, I might add), and make your stuff available easily, else you will be left behind and rightfully forgotten.

I do also have Amazon Prime, but that has enough crossover with Netflix that I mostly use the shipping benefits. If I'm looking for something, I will check CanIStream.it (aka, Don'tMakeMeFuckingPirate.It), and if it's not available on Netflix/Amazon, I'll wait. Sooner or later it will be.

...everywhere except Linux.

This isn't due to transcode issues. They use Silverlight to stream to full-function PCs (be it OSX or Windows). Microsoft hasn't made Silverlight available to the greater GNU community, so it's pretty obvious that they wouldn't distribute to Linux: their contracts with content-holders probably hold them to constricting DRM demands on the videos streamed to devices capable of ripping them off.

Don't blame Netflix for it. Blame the arduous contracts which must be negotiated in order for Netflix to carry the content it does.

They have a working Android application which uses native linux code to handle the DRM.

So Silverlight not beign supported on Linux is not the real issue here.

Right, it's the contracts, exactly like the parent post said...

The issue is it not being supported on regular desktop Linux (excl. Chrome OS).

It's all about PlayReady. PlayReady can have backings that tie into hardware protection. That is why it's available for devices that run on Linux - because MS has licensed PlayReady for those implementations. I suspect most, if not every single such device, have hardware support for DRM.

It's not native, but check out https://aur.archlinux.org/packages/netflix-desktop/ if you use Arch.

I actually did install this on my Ubuntu system, but it only gets 10-15 fps (as far as I can tell). Not quite watchable.

As technology progresses we can probably assume that at some point in the future virtually all devices in use will have fast enough network connections and decoders to play videos that are the highest quality the human eye can see. At this point it would only be worth encoding in this "highest" quality. Of course, by this time we may have new screen technologies such as holographic displays.

It will likely still be cheaper to send only as little as will actually be rendered.

Yes I can see you mean a time and day when everyone will gigabit connections and what not.

But then you're forgetting: poverty hasn't quite abandoned us yet, has it?

Even with all of the modern technology and what not -- people are still dying of hunger.

We first need to start with these base human needs.

Elevate the standard of living of the people on the other side of digital (and economic) divide, and bring them up to standard of an average first-world-country person.

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