In response to Steve Jobs' open letter about Flash last week, TechCrunch contacted encoding.com, a video encoding service, to get their statistics on what formats their clients are requesting. In Q1 2010, 66% of all videos that encoding.com processed were encoded into H.264, while On2 VP6 and .FLV (which could be any codec supported by Flash, but in this case probably means Sorenson) together add up to 26%. (Ogg Theora is barely 2%.) Here's the chart:
Keep in mind that encoding.com has encoded 5 million videos over the past year for a variety of clients, but it in no way represents the majority of video sites or content. Also, these numbers represent new or transcoded files, not the huge number of legacy video files that still exist on the web. Nevertheless, encoding.com's numbers suggest that H.264 has got major adoption momentum. However, that could change.
Google's rumored announcement later this month that it will make On2's VP8 format available as open source may change the balance, especially if YouTube starts encoding its videos in VP8. According to ComScore's traffic numbers for March, YouTube had more video viewing traffic than then next ten sites put together, so as YouTube goes, so goes a large part of the market.