A view on VP9 and AV1 part 2: important considerations
The success of a video coding standard depends on many factors. Many articles try to benchmark the performance of codec implementations or make comments about the ecosystem of codecs. But I have not seen any article about the standardization process or the bitstream format. While the video quality is key, I believe the bitstream format is important too, but is probably less accessible or easy to communicate about.
This is a two-part analysis. Part 1 compares the HEVC and VP9/AV1 codecs in the light of their bitstream formats. Part 2 (this article) will look at some other important considerations.
Video codecs: factors of success
The success of a codec is made of several components:
- Compression: the video quality at given bitrate constraints.
- Performance: how it compares to other codec implementations (in term of CPU versus quality/bitrate balance).
- A non-ambiguous specification. This requires many people to read it.
- Some tools to help editing better standards.
- A clear patent and royalty policy: of course free is better but innovation always comes at a cost.
- Simplicity to implement: too much complexity leads to incompatibilities and delays in implementations, and requires more hardware surface (hence increases the power consumption).
- Software implementations for both encoders and decoders.
- Room for hardware acceleration.
- Ability to embed in popular containers.
- Analyzers (the Google VP9 decoder comes with a nice ‘–enable-coeff-range-checking’ configure option).
- Reference vectors (it seems that fuzzing with AFL leads to more interesting vectors than what codec vendors provide).
- Competition with other codecs: having competitors helps get better.
Standardization and patents considerations
VP9 and AV1 bitstream formats are far simpler than AVC or HEVC but are also less mature. That's a consequence of the development process: VP9 was done by one company, HEVC was standardized by a consortium via a lengthy process.
In this process, many MPEG members were able to insert their patented feature. In that regards, the AV1 codec is important for the video ecosystem. The industry is poisoned by the current patent system which produces closed ecosystems, important fees and needlessly complex standards. AV1 is being backed by huge companies and patent holders. But AV1 probably also makes use of important external patents while being royalty-free. So it will be interesting to see if there will be lawsuits ; the results of these lawsuits may change the behavior of the industry.
For most managers, the video problem is considered solved and their solution is to take open-source projects such as FFmpeg, GPAC, MediaInfo and VLC to build a complete workflow. This analysis is premature in my opinion, even if many managers commonly share it. As a consequence, possible issues in VP9/AV1 are not taken seriously enough. If they were fixed, we would not be far from a convincing alternative to HEVC.
We like VP9 and AV1 for their simplicity, openness, and patent-free approach. In the Part 1 of this article, we focused on the VP9/AV1 bitstream format. We concluded that AV1 had the potential to compete with HEVC from a bitstream format point of view but still contained a few serious issues.
In this Part 2, we focused on several considerations other than quality and performance. Codecs should be evaluated with regards to their ecosystems and a strategic view: the failure of VP9 or AV1 is possible but would it be important for the AV1 supporting entities? Is this initiative a way to achieve other goals?
- https://sonnati.wordpress.com/2016/06/03/does-vp9-deserve-attention-part-i/ and https://sonnati.wordpress.com/2016/06/17/does-vp9-deserve-attention-part-ii/