AMV video format


AMV is a proprietary video file format, produced for MP4 players, as well as S1 MP3 players with video playback. There are now two different MTV formats: the older one for the Actions chip, and a newer one for ALi’s M5661 chip. This format for ALi one was ALIAVI.

Format

The container is a modified version of AVI. The video format is a variant of Motion JPEG, with fixed rather than variable quantisation tables. The audio format is a variant of IMA ADPCM, where the first 8 bytes of each frame are origin, index and number of encoded 16-bit samples ; all known AMV files run sound at 22050 samples/second.
Low decoder overhead is paramount as the S1 MP3 players have very low-end processors. Video compression ratio is low – around 4 pixels/byte, compared with over 10 pixels/byte for MPEG-2 – though as the files are of low resolution and frame rate, file sizes are small in bytes per second. With a resolution of 128×96 pixels and a framerate of 12 frame/s, a 30-minute video will be compressed into 80 MB.

Documentation

Documentation for this format is not publicly available, but Dobrica Pavlinušić reverse engineered the format to produce a Perl-based decoder and Pavlinušić, Tom Van Braeckel and Vladimir Voroshilov produced a version of FFmpeg that works on AMV files.