There is no single combination of containers and codecs that works in all HTML5 browsers.
For maximum compatibility you need more than one version:
Container: WebM
Video-Codec: VP8
Audio-Codec: Vorbis
Container: Ogg
Video: Theora
Audio: Vorbis
Container: MP4
Video: H.264 baseline-profile
Audio: AAC (low complexity)
For MP4 Mobile pay attention to possible max-resolutions on the different devices:
480×320 (base), 640×480 (no older androids, blackberrys) or more e.g. 1280×720 (only ‘new’ devices)…
More Info and references:
http://fortuito.us/diveintohtml5/video.html
http://blog.zencoder.com/2010/09/30/how-to-encode-video-for-mobile-use/
Frameworks/Libs for HTML5 implementation: