GoToMeeting Codec

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Revision as of 12:54, 8 November 2011 by Kostya (talk | contribs) (Chunk C8)
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This is a codec used to save recordings in GoToMeeting. The codec also calls itself GoToWebinar (see http://www.gotowebinar.com/).

Win32 binary decoder available here: http://www.gotomeeting.com/codec

According to samples, all G2M2 video frames begin with the characters 'G2M2', followed by a series of chunks. Each chunk has the following layout:

bytes 0-3    length of chunk payload, not including this length field
byte 4       type of chunk
bytes 5..    remainder of payload, format unknown

Supported chunk types are 0xC8-0xCD.

It appears that the minimum size for a G2M2 frame (possibly a no-change frame) is 14 bytes. This includes the 4 signature bytes, a 4-byte length indicating a chunk length of 6, and a 6-byte payload of type 0xCA followed by 5 more bytes.

G2M3 bears much similarity to G2M2 at the surface level. Naturally, each frame has a signature of 'G2M3'.

Chunk C8

This seems to contain display information.

Chunk contents (all values are big-endian):

  4 bytes  image width
  4 bytes  image height
  4 bytes  compression mode (should be 2 or 3)
  4 bytes  number of tiles in column (maybe)
  4 bytes  number of tiles in row (maybe)
  1 byte   colour depth (4, 8, 16, 24 or 32)
  for 4/8bpp there is a palette in standard RGBTUPLE format
  for 16-32bpp there are four bitmasks for each field