This file documents the simple animation format used by SMJPEG
This is for static animation files, not for audio/video streaming.

All 32-bit and 16-bit values are stored in big-endian format.

8 bytes magic - "^@\nSMJPEG"
Uint32 version = 0
Uint32 length of clip in milliseconds

One or more optional comment headers:
4 bytes magic - "_TXT"
Uint32 text length
arbitrary text

Optional audio header:
4 bytes magic - "_SND"
Uint32 audio header length
Uint16 audio rate
Uint8  bits-per-sample  (8 = unsigned 8-bit audio, 16 = signed 16-bit LE audio)
Uint8  channels         (1 = mono, 2 = stereo)
4 bytes audio encoding  ("NONE" = none, "APCM" = ADPCM compressed)

Optional video header:
4 bytes magic - "_VID"
Uint32 video header length
Uint32 number of frames
Uint16 width
Uint16 height
4 bytes video encoding  ("JFIF" = jpeg)

End of header marker:
4 bytes magic - "HEND"

Interleaved chunks of audio/video data:
4 bytes magic - "sndD" for sound data, "vidD" for video data
Uint32 millisecond timestamp
Uint32 chunk length   

// Comment -
A single video chunk corresponds to a single frame of video.
A single audio chunk corresponds to audio data not more than 4K uncompressed.
(decoders may silently truncate chunks that contain more than 4K of
 audio data, though a robust implementation would accept them.)

// Comment -
The audio/video chunks should be more-or-less ordered according to timestamp
so seeking by time works correctly.  Audio chunks should be ordered before 
video chunks, and all audio chunks for a given frame of video should be 
grouped together.  This results in good playback when scanning linearly.
i.e. AAAV-AAV-AAAV-... (A = audio chunk, V = video chunk)

// Comment -
The audio chunks should be encoded one frame ahead of the video chunks
(i.e. current frame + next frame) so that if the decoder gets behind,
the audio is queued up and doesn't underflow.  The decoder will quickly
skip the next video frame and catch up.

// Comment -
The ADPCM audio encoded chunk consists of:
Uint16 valprev
Uint8 index
Uint8 unused
... compressed audio data

End of data marker:       
4 bytes magic - "DONE"