There are a lot of variants of first two TrueMotion codecs. Final Fantasy (some number here) for PC uses TM2.
Differences from reference decoder: delta table size must be greater (64 instead of 32) and sometimes there is no data in stream, which means you should fill it with value from Huffman table).
Well, there is also TM2X awaiting.
Recent VMWare virtual machines are able to capture their screen output and store it into AVI packed with their own codec. A quick study showed that this codec stores captured image in special type blocks, most of them are labeled WMVx (maybe VMW spelled backwards, but who knows 😉 ). Every block type has its own function to handle it. Blocks with labels WMVi or 0x00000005 can be found in almost every frame.
Here are main differences between TrueSpeech and G.723:
1) One bitrate (8 Kb/s) vs. two bitrates (6.3 and 5.3 Kb/s)
2) Lower complexity (TrueSpeech uses 8-point LPC, G.723 – 10-point LPC)
Frame structure is also differs, TrueSpeech packs everything into 32 byte frame where some values are spread between different doublewords (3d bit is in one dword, 2nd is in another one).
DSP Group TrueSpeech audio codec is rumored to be a relative to ITU G.723. That may be partly true: DSP Group took part in developing G.723, but if you study recommendation G.723, you’ll see that there are two methods used in this rec., and they differ.
Studies showed that TrueSpeech may be one of predecessors of G.723 – it is simplier, needs higher bitrate than G.723 and such. But I hope to use some ideas to reconstruct TrueSpeech decoder using methods from G.723.
My TrueMotion 2 decoder is almost complete. It just has some problems with chroma decoding in intraframes. I suspect this is because of some rounding errors and such. Original TM2 decoder used to store chroma in pairs – one 4 double word for 16-bit Cr and Cb and all calculations were done on those pairs.
For now, I’ll leave this decoder for some time and will post pieces of information about other codecs.