OP implements their own RLE-based compression scheme. I bet you'd get better results from emitting an uncompressed binary format, and then passing the whole thing through a general-purpose compressor like zstd.
I'd also be interested to see what zstd (or even just gzip) would make of their original un-optimised format - I bet you'd get most of the way there "for free".
I'd also be interested to see what zstd (or even just gzip) would make of their original un-optimised format - I bet you'd get most of the way there "for free".