Monday, August 02, 2010

Extensive VP8/H.264 Comparison from Jan Ozer

Jan Ozer and have done an extensive follow-up to their earlier comparison of VP8 (the video codec within Google's open-source WebM) and H.264. I'll briefly summarize their findings:
  • In general, the playback CPU utilization of VP8 and H.264 are almost identical. However, many PCs and other devices have H.264 hardware acceleration; on those platforms, H.264's CPU utilization will be much less than that of VP8. This difference will continue until Google gets vendors to make VP8 hardware acceleration standard.
  • VP8 requires much longer encoding times than H.264, but the difference can largely be mitigated by using an encoder that supports multiple cores and threads.
  • Ozer compared the subjective output quality of Sorenson Squeeze's VP8 encoder, X264 and MainConcept's H.264 encoder. He concluded that X264 output looked best, followed by H.264 and then VP8. However, he noted that the differences between the three encoders were so small as to be virtually unnoticeable except in side-by-side testing.
  • Ozer's conclusion: H.264 will remain royalty-free for free Internet content until 2015, and hardware acceleration for VP8 will take a long time to become widespread, so he sees no need for producers or distributors of free Internet content to switch. (He doesn't address the issue of paid content, and that's where VP8 is likely to have more impact when it's more widely adopted by encoder and browser vendors.)
Ozer also points to an extensive analysis by Jason Garrett-Glaser, one of the developers of X264. Garrett-Glaser's bottom line is that the encoding quality of VP8 is about the same as H.264 Baseline Profile and considerably less than Main or High Profile. He expects the decoding performance of VP8 and H.264 to be about the same, but that H.264 will have a significant advantage because of broad support for hardware acceleration of H.264 decoding.

Perhaps most significantly, Garrett-Glaser questions the claims that VP8 is patent-free; he believes that VP8 and H.264 use similar techniques in many parts of the encoding process. In fact, he says that calling VP8 "H.264 with a better entropy coder" would be an only slightly inaccurate description.

My bottom line? If you're producing or distributing free video content only, there's no reason to deal with VP8 or WebM for now. It's going to take at least a year for Google and its partners to optimize encoding and decoding and start getting VP8 hardware acceleration built into GPUs and other devices, and to resolve whether or not VP8 is truly patent-free. Unless you're an encoder, decoder or accelerator developer, I'd let these issues shake out before you adopt VP8 and WebM.
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