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| AMV video format ： ウィキペディア英語版 |
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.〔(forcing mjpegenc to use fixed quantisation tables ) (Tom Van Braeckel, FFmpeg-devel mailing list, 28 October 2007)〕 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.〔
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〔 – 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.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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