Psygnosis YOP: Difference between revisions
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* Extension: yop | * Extension: yop | ||
* Company: [[Psygnosis]] | * Company: [[Psygnosis]] | ||
* Samples: http://samples.mplayerhq.hu/game-formats/yop/ | |||
YOP is an [[FMV]] video format used in the computer game [http://www.mobygames.com/game/city-of-lost-children The City of the Lost Children] by Psygnosis. Based on the very primitive pattern-based video compression and stock [[IMA ADPCM]] sound encoding. | YOP is an [[FMV]] video format used in the computer game [http://www.mobygames.com/game/city-of-lost-children The City of the Lost Children] by Psygnosis. Based on the very primitive pattern-based video compression and stock [[IMA ADPCM]] sound encoding. | ||
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[[Category:Game Formats]] | [[Category:Game Formats]] | ||
[[Category:Video Codecs]] | |||
[[Category:Formats missing in FFmpeg]] |
Revision as of 15:00, 31 January 2008
- Extension: yop
- Company: Psygnosis
- Samples: http://samples.mplayerhq.hu/game-formats/yop/
YOP is an FMV video format used in the computer game The City of the Lost Children by Psygnosis. Based on the very primitive pattern-based video compression and stock IMA ADPCM sound encoding.
File Format
File begins with the following 2048-bytes header:
+ 0 word Signature -- "YO" + 2 byte Unknown_2 -- unused, but set to 1. Perhaps format version + 3 byte Unknown_3 -- unused, can be either 0 or 1. Format version minor? + 4 word NumFrames -- number of frames + 6 byte Unknown_6 -- framerate? + 7 byte FrameSize -- size of the single frame chunk in sectors (2048 bytes per sector) + 8 word Width -- frame width + A word Heigth -- frame height + C byte PalColors -- number of colors in palette per frame *see notes* + D byte FirstColor1 -- first color to update for odd frames (counting from 1) + E byte FirstColor2 -- first color to update for even frames (counting from 1) + F byte Unknown_C[3] -- unused/zero + 12 word SoundLen -- size of the audio block for frame + 14 byte Unknown_14[] -- unknown/unused/padding to the next sector's boundary +800 FRAME Frames[NumFrames] -- video frames
For each frame:
+ 0 dword Unknown_0 -- unused/ignored, some length? + 4 RGB Palette[PalColors] -- palette part for this frame, 6 bits per component +xxx byte Sound[SoundLen] -- ADPCM-encoded sound data, mono, 22050Hz, 1840 samples per frame +yyy byte Video[...] -- encoded video data, variable length +zzz byte Padding[...] -- unused/padding ---- total frame size is FrameSize * 2048
- All numbers are little-endian.
- Both file header and each frame chunk are aligned/padded to the 2048-bytes boundary.
- Worse, frame chunks has fixed size (FrameSize * 2048), even if the actual payload size is much smaller.
- Each frame comes with it's own palette part, updating PalColors entries starting from FirstColor1 for odd and FirstColor2 for even frames respectively.
- IMA decoding context initialized to zero at the beginning of the playback and then updated by successive frames
Video Compression
Video frame broken on 2x2 macroblocks and each macroblock decoded using the following algorighm:
tag = next nibble tag is: 0 : abcd 1 : abca 2 : abcb 3 : abcc 4 : abac 5 : abaa 6 : abab 7 : abbc 8 : aabc 9 : aaba A : abba B : aabb C : aaab D : aaaa E : abbb F : read next tag and copy previously drawn block located at the following coordinates (in pixels) relatively to the current block: tag is: 0 : -4:-4 1 : -2:-4 2 : 0:-4 3 : 2:-4 4 : -4:-2 5 : -4: 0 6 : -3:-3 7 : -1:-3 8 : 1:-3 9 : 3:-3 A : -3:-1 B : -2:-2 C : 0:-2 D : 2:-2 E : 4:-2 F : -2: 0
- abcc means "read byte a and use it to paint pixel 1 (top left), read byte b and paint pixel 2 (top right), read byte c and paint pixel 3 (bottom left) AND pixel 4 (bottom right)".
- Tags are 4-bit nibbles, processed starting from the high one (bits 4..7), then lower (bits 0..3). However, complete byte read first, thus pixel bytes do not overlapped with the tags.