My friend Jan has published some quality comparisons between the Ogg and H.264 video codec. For those who don't know, Ogg Theora is the video container format and codec favoured by Mozilla for playback of web video in HTML5 whereas H.264 is a widely popular codec - one may say the industry standard - that is used for all types of content from Flash (on sites that include YouTube and Hulu) to Blu-Ray and DVB broadcast television.
I can't say that I'm surprised about Jan's test results in which H.264 comes out on top. Ogg Theora is quite a dated codec which is based on Ons'2 VP3 specs, and which has become a free, open standard. Unfortunately the label of free software alone does not guarantee that Ogg Theora won't be vulnerable to yet unknown patents. For those reasons I would personally be very surprised if Ogg Theora sees any significant uptake in the future, even once HTML5 becomes more widely supported. Major players such as Apple and Nokia were amongst those who opposed the inclusion of this specific format as part of the proposed HTML5 specs, and it is highly doubtful that Mozilla alone has enough leverage to give this compression format a new lease of life.
Meanwhile both Safari and Chrome are focused on supporting H.264 which they consider to be a better choice for web video.
Check Jan's full article here and stay tuned for some more video codec specific tests in the coming weeks.