Since I had nothing better to do I’ve documented various ARMovie codecs in The Wiki. Essentially what’s left is to document newer Moving Blocks variants (and implement a decoder for one with samples), early Eidos Escape codecs (no idea where to find samples for them though). Also there’s Iota Software codec 500 which has no samples but looks like it’s used primarily in ACE Film format so figuring out nuances of LZW compression there may help with yet another obscure format.
From the technical side the most annoying thing is that data is stored in multiple frames in a single chunk without any kind of size, separator or frame end marker being present. The original player simply expected decoders to report number of bytes consumed after decoding a frame. Which means packetisers that should parse the stream in the same way as decoders do and report the frame size—nothing too complex but still annoying (and I had to augment NAPacketiser API to take reported stream details into account, otherwise it has no way to know frame dimensions). The worst one was Moving Blocks parser. The main problem is that unlike most of the formats this one has frames not aligned to 16 bits—while video chunks are—so it has to deal with possible padding byte at the end of chunk.
Another annoying thing I haven’t really dealt with is detecting all those various sound formats from the format string.
I don’t know if I bother adding various raw video formats support but in either case I don’t regret looking at ARMovie. Even simple codecs turned out to be not so simple and sometimes with interesting peculiarities like run of colour pairs and even four-colour pattern painting in what should’ve been a simple RLE codec.