Using 16:9, MPEG4, H.264 video, AAC audio, automatic keyframes for everything (except FLV for the low resolution Flash).
iTunes HD (download) - 720p>4 Mbps total.
Video: 25fps, 1280x720. 'High' profile. Multi-pass, optimised for download.
Audio: 128kbps, stereo.
iTunes SD (download, podcast, iPod, bundled with HD) - 480p1.5Mbps total.
Video: 1408kbps, 25fps. 640x360. 'Baseline' profile. Multi-pass, optimised for download (optimise for streaming (constant bitrate) only if there are high-bitrate sections that pass the peak bitrate playable by the iPod).
Audio: 128kbps, stereo, AAC-LC.
Progressive download (Flash player (high resolution), Second Life, QuickTime browser plugin, iPhone)512kbps total.
Video: 448kpbs, 25fps. 480x272, or letterboxed 480x320 for compatibility. 'Baseline' profile. Multi-pass, optimised for download (variable bitrate; optimise for streaming only if using RTSP and need to enforce a steady bitrate). "Fast Start for internet streaming" if making a QuickTime movie.
Audio: 64kbps. Mono where possible, otherwise stereo.
Live streaming (Second Life, etc)256kbps total.
Video: 192kbps, 320x240 (this is 4:3, for streaming from a webcam/camcorder), 15fps.
Audio: 64kbps, mono.
FLV (Flash Player (low resolution))On2 Flix VP6 encoder?
I'd be very interested in knowing if anyone has improvements to these settings.