While researching the formats to support I’ve finally encountered an animation format for CGA, from the times when H.261 was ratified (i.e. 1988) but a bit simpler than that format.
Essentially it’s RLE-compressed CGA memory buffers either in 640×400 monochrome or 320×200 eye-gouging 2-bit colour mode. RLE has a twist as instead of the usual mode switch or symbol repeating it sends the list of symbols that have run lengths after them.
The hardest part was to actually render the resulting frame. For some reason CGA video modes organisation is not as widely documented as EGA or VGA, and it differs enough from them. The 256-colour VGA mode is simple: there are four planes responsible for interleaved parts of the frame or you can even simply pretend it’s one contiguous blocks (with VLB and 80486 you probably won’t care about hidden performance hit anyway). EGA as many video formats of the era (like Amiga but not as exquisite; and most of VGA modes as well) simply separates data into bit-planes. CGA on the other hand first splits data into even/odd lines using two different pages for that and packs bits continuously. I can guess what technical limitations made it work this way but I still don’t like the result.
Anyway, I think this obscure format from the past really stands out and deserves a mention at least somewhere (like this blog). Oh, and README.TXT mentions the program was written by an attorney—I don’t know what aspect of it all is merely mundane.