TrueMotion 1 was licensed and has several variants outside the usual TM1. There’s allegedly Horizons PowerEZ but only j-b would know anything about it—because it’s vintage and used to code content he’s interested in of course. The other version was used for intro and victory cutscenes in Star Control II: Ur-Quan Masters 3DO version, the source code is available so any Mike Melanson out there can have a look at it. To me it looked as the same coding algorithm but with custom delta tables and codebooks provided. Oh, and data is split between several files (global header, codebook, frame data and offsets to individual frames).
TrueMotion 2 Realtime seems to be really Truemotion 1.2 Realtime Edition. It has quite similar header format to TrueMotion 1 (same obfuscation even) but with some values that would make TM1 decoder bail out on error and it was released before actual TrueMotion 2.
TrueMotion 2X seem to return to coding method from TM1 as well since there’s a suspicious similarity between its inverse Huffman coding method (they call it “string encoder” which sounds somewhat even more confusing) and the codebook used in TM1 except that in TM2X they use 0x80 as the end of data flag instead of 0x01.
P.S. I should really move to VP4 and then away from this codec family altogether.
I think the TM1 variant in Star Control II is the earliest known version of TM1 in the wild.
The people making the open source Ur-Quan Masters asked me a question about it many years ago… and for that, I got a mention in the credits.
And for that, I get to have a developer credit in the MobyGames database, so that’s my claim to fame!