H.264 x Webm - Porque o codec padrão do Google (Youtube) é uma porcaria
Autor: Maurício Menon | Publicado: 2011-04-22T18:19:00-03:00

Texto completo em:&nbsp;http://x264dev.multimedia.cx/archives/377


Overall verdict on the VP8 video formatOverall, VP8 appears to be significantly weaker than H.264 compression-wise.&nbsp;The primary weaknesses mentioned above are the lack of proper adaptive quantization, lack of B-frames, lack of an 8×8 transform, and non-adaptive loop filter. With this in mind, I expect VP8 to be more comparable to VC-1 or H.264 Baseline Profile than with H.264. Of course, this is still significantly better than Theora, and in my tests it beats Dirac quite handily as well.
Supposedly Google is open to improving the bitstream format — but this seems to conflict with the fact that they got so many different companies to announce VP8 support.&nbsp; The more software that supports a file format, the harder it is to change said format, so I’m dubious of any claim that we will be able to spend the next 6-12 months revising VP8.&nbsp; In short, it seems to have been released too early: it would have been better off to have an initial period during which revisions could be submitted and then a big announcement later when it’s completed.
Update: it seems that Google is&nbsp;not&nbsp;open to changing the spec:&nbsp;it is apparently “final”, complete with all its flaws.
In terms of decoding speed I’m not quite sure; the current implementation appears to be about 16% slower than ffmpeg’s H.264 decoder (and thus probably about 25-35% slower than state-of-the-art decoders like CoreAVC). Of course, this doesn’t necessarily say too much about what a fully optimized implementation will reach, but the current one seems to be reasonably well-optimized and has SIMD assembly code for almost all major DSP functions, so I doubt it will get that much faster.
I would expect, with equally optimized implementations, VP8 and H.264 to be relatively comparable in terms of decoding speed. This, of course, is not really a plus for VP8: H.264 has a great deal of hardware support, while VP8 largely has to rely on software decoders, so being “just as fast” is in many ways not good enough. By comparison, Theora decodes almost 35% faster than H.264 using ffmpeg’s decoder.
Finally, the problem of patents appears to be rearing its ugly head again.&nbsp;VP8 is simply way too similar to H.264: a pithy, if slightly inaccurate, description of VP8 would be “H.264 Baseline Profile with a better entropy coder”. &nbsp; Even VC-1 differed more from H.264 than VP8 does, and even VC-1 didn’t manage to escape the clutches of software patents.&nbsp; It’s quite possible that VP8 has no patent issues, but until we get some hard evidence that VP8 is safe, I would be cautious.&nbsp; Since Google is not indemnifying users of VP8 from patent lawsuits, this is even more of a potential problem.&nbsp; Most importantly, Google has not released any justifications for why the various parts of VP8 do not violate patents, as Sun did with their OMS standard: such information would certainly cut down on speculation and make it more clear what their position actually is.
But if luck is on Google’s side and VP8 does pass through the patent gauntlet unscathed, it will undoubtedly be a major upgrade as compared to Theora.