- Company: The Company of Science and Art
The format comes from Macintosh so all values are big-endian.
2 bytes - 0x0001 2 bytes - 0x0026 2 bytes - width 2 bytes - height 2 bytes - framerate (negative means there's no audio stream) 2 bytes - flags? 4 bytes - maximum chunk size 4 bytes - always zero? 4 bytes - something audio-related 2 bytes - number of chunks 2 bytes - number of chunks repeated 2 bytes - always 8? 2 bytes - always 0x600? 4 bytes - some flags 2 bytes - always 0?
The header is followed by 32-bit chunk sizes. After that actual chunks data is present.
Each chunk consists of several records with 4-byte header (1 byte - record type, 3 bytes - record size including the header). Known record types are:
- 0 - nop
- 1 - old initialisation data?
- 2 - new initialisation data (usually
0x30 0x00 0x00 ...meaning 8-bit with default QuickTime palette)
- 3 - delay information
- 4 - audio data (8-bit unsigned PCM)
- 5 - should not be present
- 6 - should not be present
- 7 - unknown
- 8 - video frame
- 9 - unknown
- 10 - dummy?
- 11 - end of chunk marker
Video compression is an enhanced RLE scheme.
Frame data starts with the following header:
2 bytes - x offset of the updated area 2 bytes - y offset of the updated area 2 bytes - updated area width 2 bytes - updated area height 1 byte - compression method and flags 1 byte - padding
Compression method should be 1 or 2, known flags are
0x20 - frame uses compact RLE and
0x40 - delta frame.
Compression methods 1 and 2 are the same except that the latter codes picture in interlaced manner (i.e. first it decodes all even lines of the updated area and then all odd lines). RLE compresses each line separately so no run/copy/skip should go past the line end.
Compression format uses the following opcodes:
0x00- long operation
0x7F- copy the same amount of pixels
0xFD- repeat the following value
256 - optimes
0xFE- next byte is either the number of pixels to skip (if non-zero) or a signal of compact RLE mode
0xFF- pair or quad run. Read the next byte and if it is below 128 then read and repeat a pair of pixels
lentimes, otherwise read and repeat four pixels (but
256 - lentimes)
Long operation (opcode
0x00) has 16-bit word specifying the actual operation (top nibble) and operation length (bottom 12 bits). Known operations are:
- 0 - raw copy pixels
- 1 - RLE
- 2 - pair RLE (read a pair of pixels and repeat it the specified number of times)
- 3 - quad RLE (read four pixels and repeat it the specified number of times)
- 4 - skip
- 5 - end current line and skip additional
- 15 - not real opcode but
00 F0 00 00is often seen at the end of frame and can serve as an end marker
Compact RLE mode works until the current line end but using nibbles to code lengths and operations and maintaining a set of 16 colours that should be used and transmitting their indices instead. Right after
FE 00 there is 16-bit mask telling which colours in the set should be updated (least significant bit - first colour, top significant bit - last colour). After the mask and optional update colours actual compact opcodes follow.
Compact mode opcodes:
0x- low nibble is the actual operation, the following byte is operation length. Operations are: 0 - copy, 1 - run (colour index is in low nibble), 2 - pair run, 3 - quad run, 4 - skip, 5 - end of line (plus skipping additional lines);
7x- copy 1-7 colours with the corresponding nibble indexes from the stream, low nibble of opcode byte is the first index. If the number of colours is even it is padded to the byte with zero nibble.
Dx- repeat colour with low nibble index
16 - (op >> 4)times
Ex- skip the number of pixels in low nibble
Fx- pair or quad run (if low nibble is less than eight then it's a pair run, otherwise it's a quad run for
16 - (op & 0xF)times).