It looks like FFmpeg does support reading from sockets natively[1], I didn't know that. That might be a better solution in this case, I'll have to look into some C code for writing my output to a socket to try that some time.

[1] https://ffmpeg.org/ffmpeg-protocols.html#unix

Why should sockets be faster?

Sockets remap pages without moving any data while pipes have to copy the data between fds.