As I said in the previous post, I was looking at PACo format with an enhanced RLE compression. It turned out to be even more curious than I expected.
Beside the normal RLE mode it has pair and quad RLE (where you repeat two or four pixels) and long operation mode where you can do single/pair/quad RLE, copy or skip using 12-bit number. But it turns out it also has a compact RLE mode that works on a single line using a set of 16 colours and putting operation code, length and colour index into a single nibble instead of a byte (and it also has its own long mode where lengths are using a whole byte!).
That’s the variety I miss in modern video codecs.
You’re a machine!