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.

AMV
Filename extension
.amv, .mtv
Container forAudio, video
Extended fromAVI and Motion JPEG
Standardproprietary

Format

The container is a modified version of AVI.[1] The video format is a variant of Motion JPEG, with fixed rather than variable quantisation tables.[2] The audio format is a variant of IMA ADPCM, where the first 8 bytes of each frame are origin (16 bits), index (16 bits) and number of encoded 16-bit samples (32 bits); all known AMV files run sound at 22050 samples/second.[1]

Low decoder overhead is paramount as the S1 MP3 players have very low-end processors (a Z80 variant). Video compression ratio is low – around 4 pixels/byte, compared with over 10 pixels/byte for MPEG-2[1] – though as the files are of low resolution (96×96 up to 208×176) and frame rate (10, 12, or 16 frame/s), 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[1] to produce a Perl-based decoder[3] and Pavlinušić, Tom Van Braeckel and Vladimir Voroshilov produced a version of FFmpeg that works on AMV files.[4]

gollark: CDs might, though.
gollark: See, digital audio would never do this unless your software is wrong.
gollark: I mean, generally bad, possibly very bad, I don't really know.
gollark: Burns are possibly bad, after all.
gollark: It seems a reasonable thing to say, really.

References
  1. voroshil (2007-10-15). "AmvDocumentation". Google Code. Archived from the original on 23 March 2008. Retrieved 2008-04-06.
  2. forcing mjpegenc to use fixed quantisation tables (Tom Van Braeckel, FFmpeg-devel mailing list, 28 October 2007)
  3. AMV free decoder (Dobrica Pavlinušić, personal blog, 19 August 2007)
  4. amv-codec-tools (Google Code)


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