SEQ

2007-04-11T00:56:53Z

Ng2C6t:

* Extension: seq

SEQ files are an [[FMV]] format used in the game [http://www.mobygames.com/game/dos/flashback-the-quest-for-identity Flashback: The Quest for Identity].

These files always contain one video stream in own format with image size 256x128 and 22 kHz 16-bit mono [[PCM]] audio.

== File Format ==
Data is stored in 6144-byte frames without any header. Each frame may contain sound data, palette data and up to 3 video frames data.
Frame structure:

bytes 0- 1 - sound data offset (0 = no sound)
bytes 2- 3 - palette data offset (0 = no palette)
byte 4 - what buffer to use (255 = skip)
byte 5 - frame num 1
byte 6 - frame num 2
byte 7 - frame num 3
bytes 8- 9 - video data offset 1
bytes 10-11 - video data offset 2
bytes 12-13 - video data offset 3
bytes 14-15 - video data end

== Video Codec ==
Frame data is divided into 8x8 blocks, each block may be compressed with one of four methods. Those 2-bit method indices are packed in 16-bit little-endian words and stored in frame header.
Methods:
* 0 - skip block
* 1 - most advanced coding mode. Data may be packed with RLE scheme described below or vector quantization (lookup table and 1-4 bits on index)
* 2 - raw block
* 3 - partial update of block, data is stored in pairs (skip, value) where skip = (x y*8 last*128), if last = 1 then end decoding, else put (value) at position (x,y)

=== RLE Packing ===
RLE data is also stored operations first, pixel data later. Operation byte consists of two signed nibbles, each meaning:
if (n < 0) then set (-n) pixels to the next value
else read (n) pixels values

[[Category:Video Codecs]]
[[Category:Game Formats]]

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SEQ