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11 December 2018

First release of dav1d, the AV1 decoder

tl;dr: dav1d has now a first release

If you want a quick summary of this post, about our AV1 decoder:

  • dav1d is good enough that it has an official release,
  • dav1d now covers all the spec and features of AV1 (including 12bits),
  • dav1d is very fast on modern desktop and it is getting faster on mobile chips.

Read the following for more details...

A few reminders about dav1d

If you follow this blog, you should know everything about dav1d.

AV1 is a new video codec by the Alliance for Open Media, composed of most of the important Web companies (Google, Facebook, Netflix, Amazon, Microsoft, Mozilla...).

AV1 has the potential to be up to 20% better than the HEVC codec, but the patents license is totally free, while HEVC patents licenses are insanely high and very confusing.

The reference decoder for AV1 is great, but it's a research codebase, so it has a lot to improve.

Therefore, the VideoLAN, VLC and FFmpeg communities have started to work on a new decoder, sponsored by the Alliance of Open Media, in order to create the reference optimized decoder for AV1.

Release

Today, we release the first usable version of dav1d, called 0.1.0, Gazelle.
It means you can use the API, ship the decoder, and expect a bit of support on it.

We launched dav1d, more than 2 months ago, during VDD, and we've been working a lot since:

  • we support all the features of AV1, even the less known ones,
  • we support, 8, 10, 12 bits, and all chroma subsamplings,
  • we support all AV1 files that were shared to us,
  • we spent a lot of time to make dav1d very fast, while keeping the binary size manageable.

On modern desktop, dav1d is very fast, compared to other decoders:

You can see more details on my previous post.

More performance to come.

But, since the previous blogpost, we've added more assembly for desktop, and we've merged some assembly for ARMv8, and for older machines (SSSE3).

We're now as fast as libaom, in single-thread, on ARMv8, and faster with more threads.

We've been also merging more SSSE3 code. (I haven't had enough time to bench it).
Which means that we will soon be faster than other decoders, on all platforms.

And, we've been experimenting with shaders, notably for the Film Grain feature.

Get it

You can get the tarball on our FTP: dav1d 0.1.0.

You can get the code and report issues on our gitlab project.

You can also join the project, or sponsor our work, by contacting me :)

21 November 2018

dav1d: performance and completion of the first release

tl;dr: dav1d is in a very good shape

If you want a quick summary of this post:

  • dav1d now covers all the spec and features of AV1, for 8bits and 10bits depth,
  • dav1d is very fast, up to 400% faster (more fps) than the libaom decoder, and very often 100% faster.

Now is the right time to integrate it, in your products!

Read the following for more details...

A few reminders about dav1d

AV1 is a new video codec by the Alliance for Open Media, composed of most of the important Web companies (Google, Facebook, Netflix, Amazon, Microsoft, Mozilla...).

AV1 has the potential to be up to 20% better than the HEVC codec, but the patents license is totally free, while HEVC patents licenses are insanely high and very confusing.

The reference decoder for AV1 is great, but it's a research codebase, so it has a lot to improve.

Therefore, the VideoLAN, VLC and FFmpeg communities have started to work on a new decoder, sponsored by the Alliance of Open Media, in order to create the reference optimized decoder for AV1.

Features

We launched dav1d, exactly 2 months ago, during VDD.

We did a lot of work since. And by "we", I mean mostly the others. :)
There are now more than 500 commits from 29 contributors from different open source communities. This is a good result for a new open source project.

First, we've completed all the features, including Film Grain, Super-Res, Scaled References, and other more obscure features of the bitstream. This covers both 8 and 10bits, of course.
We also improved the public API.

Then, we've fuzzed the decoder a lot: we are now above 99% of functions covered, and 97% of lines covered on OSS-FUZZ; and we usually fix all the issues in a couple of days. This should assure you a secure decoding for AV1.

Finally, we've written a lot of assembly, mostly for modern desktop CPUs, but the work has been started for mobile and older desktop CPUs.
We even reduced the size of the C code!

Performance

Today, dav1d is very fast on AVX2 processors, which should cover a bit more than 50% of the CPUs used on the desktop. We wrote 95% of the code needed for AVX2, but there is still a bit more achievable.

We're readying the SSE and the ARM optimizations, to do the same. They will be very fast too, in the next weeks.

The following graphs are comparing dav1d and aomdec top-of-the-tree on master branches. (and yes, aomdec has CONFIG_LOWBITDEPTH=1).
This was done on Windows 10 64bits, using precompiled binaries.

The clips are taken from Netflix, Elecard, and Youtube, because they don't use the same parameters in the encoder, and don't have the same bitstream features.
Film Grain is not run on the CPU, so it is not visible here.

Haswell

Here, on Haswell (i7-4710, a 4 year old CPU with 4 cores), are the results:

And reported to in percentage compared to libaom:

We got in average 2.49x, and we even get 3.48x on the Youtube Summer clip!

Zen

With a more modern Zen machine (Ryzen 5 1600, 6 cores HT), here are the results:

And reported to in percentage compared to libaom:

The average is even higher at 3.49x, and we even get 5.27x on the Youtube Summer clip!

Global comparison

If we put both on the same graphs, here is what we have:

Threading

If you listened to our talks during VDD or during demuxed, we explained that dav1d threading was quite innovative, and should scale way better than libaom.

On an even less powerful machine, an i5-4590, with 4 cores/4 threads, here are our results, for the Youtube Summer clip:

You see that dav1d can scale better, in terms of threading, than libaom.

Conclusion

dav1d is very fast, dav1d is almost complete, dav1d is cool.

We're finishing the rough edges for a release soon, so that we can hope that Firefox 65 will ship with dav1d for AV1 decoding.

On the other platforms, SSE and ARM assembly will follow very quickly, and we're already as fast on ARMv8. Stay tuned for more!

I would like to thank Ewout ter Hoeven (EwoutH) from the community who did all the testing, numbers and computations.

1 October 2018

Introducing dav1d: a new AV1 decoder

Introducing dav1d

AV1 is a new video codec by the Alliance for Open Media, composed of most of the important Web companies (Google, Facebook, Netflix, Amazon, Microsoft, Mozilla...).

AV1 has the potential to be up to 20% better than the HEVC codec, but the patents license is totally free, while HEVC patents licenses are insanely high and very confusing.

The reference decoder for AV1 is great, but it's a research codebase, so it has a lot to improve.

Therefore, the VideoLAN, VLC and FFmpeg communities have started to work on a new decoder, sponsored by the Alliance of Open Media.

The goal of this new decoder is:

  • be small,
  • be as fast as possible,
  • be very cross-platform,
  • correctly threaded,
  • libre and (actually) Open Source.

Without further ado, the code: https://code.videolan.org/videolan/dav1d

Name

dav1d is called dav1d, because Dav1d is an AV1 Decoder

(Yes, that is a recursive acronym, no need to tell us...)

Video

You can see a talk during VDD 2018 about dav1d:

VDD2018 dav1d presentation.

Technical details

Some technical details about dav1d:

  • written in C99 (without VLAs),
  • has asm in NASM/GAS syntax (no intrinsics),
  • uses meson/ninja as buildsystem,
  • currently works on x86, x64, ARMv7, ARMv8,
  • runs on Windows, Linux, macOS, Android, iOS,
  • licensed under BSD.

Performance

Currently the source code of dav1d is 1/10th of lines of code compared to libaom and its weight is 1/3rd of the binary size of libaom.

It currently uses 1/4th of the memory usage of libaom and uses a very limited amount of stack.

Depending on the threads conditions (see the video talk linked above), dav1d is more or less faster than libaom 1.0.0, but slower than libaom HEAD.
dav1d having almost no assembly code yet, this is not surprising, and is actually a good starting point for the future.

Of course, those metrics will evolve once we add more assembly code, and when the project evolves a bit more.

Questions

Is it production-ready?

Not yet, but you can start testing it and check how the API works for you.

Can I help?

Yes! We need C, ASM developers, but also app integrators and testers to give us feedback.

I need to ship an AV1 decoder with my OS, my hardware, my app. Can I do that?

Yes. dav1d is licensed under BSD for this very reason.

Please talk to us, if you need to get adaptations for your use-case (hybrid decoders, or specific platforms, for example).

BSD is not copyleft, why?

We want AV1 to be as popular as possible. This requires fast decoders, running everywhere. Therefore, we want to help everyone, even non-open-source software.

See RMS opinion on this subject.