The forum thread is here - warnings: 1) it's quite long 2) it's quite technical and 3) it's cross platform, looking at both Windows Mobile and Symbian OS (represented by the Nokia N95). Oh, and 4) you'll come across the same 'bible' posting on several other prominent sites, since Menneisyys has been cross-posting it quite widely.
Notwithstanding the above, he does make some good points, in addition to the over-exhaustive research. Principally that there's a lot more to playing back digital video than you might think. A couple of points I took from his pieces:
- There are significant quality improvements to be had from H.264, compared to baseline MPEG-4. This was one of the factors which caused me to switch to it for my Smartphones Show, by the way. However, the quality improvements come at the price of increased file complexity, extra decoding filters and a lot greater load on the portable device's processor, resulting in stuttering and other unwanted interruptions. Depending on the playback software used, you may be able to disable some of these extra filters to reduce processor load, but you're then largely back to MPEG-4 baseline quality...
- Bitrate and resolution are huge factors to take into account when decoding video files, a message I've been trying hard to bang home for a while now. You can't just bung a TV resolution DivX on most smartphones and expect them to cope. Some will if they are fast enough and with powerful enough graphics chips, but the majority won't. And why should they? You're giving them four times as many frame pixels to decode as they need - a custom converted (and there are plenty of free smartphone video converters out there now) QVGA video will play far more reliably and smoothly than a VGA or DVD rip at full resolution, however clever the playback software (e.g. CorePlayer). (It's also extremely inefficient storing videos at desktop resolution on a smartphone's memory card)
I realise this is a contentious subject though. Further discussion welcome in the original thread!