I looked through the faf client github. From what I can gather the replay header ends with the first '\n' character. Following the new line are the compressed bytes. I tried using the zstd terminal tool and even compiled the zstd library to try streaming decompression like the one used in the github (although there apache commons is used and I have no idea how that is implemented). I assume that maybe there is a byte at the start or the end which I'm not removing and that is causing the problem but I really don't know. Can anybody help?
I can't decompress replay files with zstd compression
I wrote a command line utility that can unpack replays. https://gitlab.com/Askaholic/faf-replay-parser#unpack
It can do both the old version 1 format (base64 and inflate) and the new format (zstd). You can find a pre compiled Linux binary in the CI build artifacts. It can also be compiled for windows but I don’t have a ci for that.
Also the source code for the conversion is here: https://gitlab.com/Askaholic/faf-replay-parser/-/blob/60b4db37016cbe81f0f02b547fd100ed91f70571/src/faf.rs#L15