That doesn't help send multiple files over a single pipe. You can't just cat them.

You can `tar` them though :)

That's true, although that requires storage on the other end. Not too much of a problem in most cases, perhaps.

But with single input, single output, you can just do:

  ssh destination "ffmpeg -switches" <infile >outfile

you can xargs your files and even parallelize (read the xargs man page) before you ssh.

Great point! Something like this could work, modulo ffmpeg arguments which I didn't check.

    find . -name '*.mkv' \
      -exec bash -c \
        "ssh server ffmpeg < {} > {}.transcoded.mp4" \;