alt Hacker NewsI've been meaning to build exactly this for a while, and my waiting has been rewarded by someone else doing it!
Had you thought about using FUSE on the server side, rather than patching ffmpeg? Like a reverse sshfs? That avoids patching the ffmpeg binary, which allows usage of wierd and wonderful ffmpeg binaries with other people's patches.
I'd be interested in seeing how well it works with SBC GPUs - many have hardware decoding and encoding, and their vendors love to fork ffmpeg.
I've explored sftp since ffmpeg has built-in support for it (-i sftp://...), but the support is quite buggy in code, I hope to submit some patches upstream to be able to change it. FTP in contrast seemed much more stable, at least looking at the code. FTP had some other shortcomings that made it undesirable for my usecase.
That was the one motivation, the other one was that it would require rewriting arguments going into the server. What you're describing was essentially what ffmpeg-over-ip v4 (and its earlier versions!) was, and the constant feedback I'd heard was that sharing filesystems is too much work, ssh servers on windows and macOS are a bad experience, people want to use a bundled solution.
Forking ffmpeg was no easy task! Took forever to figure out the build process, eventually caved in and started using jellyfin build scripts, but that has the downside of being a few versions behind of upstream HEAD.