- FOURCCs: TM2A, TM2X
- Company: On2 (formerly Duck)
- Sample: http://samples.mplayerhq.hu/V-codecs/TM2a.avi
- Sample: http://samples.mplayerhq.hu/V-codecs/TM2x.avi
Duck TrueMotion 2X is believed to be related to Duck TrueMotion 2.
Each frame consists of chunks with the following structure:
0-2 always 0xA0 0x00 0x01 3 chunk identifier 4-7 chunk size (big-endian) 8-... chunk payload
Analyzed frames have chunks in the following order:
0x06(usually takes more than a half of coded frame)
0x15- small, variable size
0x09- 3 bytes long
0x02- two chunks of variable size
0x0B- there are always 16 of them with size=4. Maybe for some Huffman tables?
0x0A- variable size
In order to ease reverse-engineering Duck seemed to used pseudo-encryption on data. Pseudo-encryption means XORing some chunks with parts of LFSR which may be updated before some chunks. Register data is stored as big-endian number and looks like first 4 bytes of
0x06 chunk are used to initialize it (it also seems to be that chunk size minus four bytes).
LSFR update algorithm:
calculate sum by modulo 2 of bits 31, 21, 3 and inverted bit 0 shift register contents left by one bit and store new sum in LSB repeat 4 times