[FFmpeg-user] can't pipe into into ffmpeg from mp4's

[Brian Quandt]

I'd like to do the following:

This works fine:
ffmpeg -i file.mp4 towhatever.ext

however, this fails

cat file.mp4 | ffmpeg -i - towhatever.ext

I know the reason, ie mp4's (QT's) have their file information at the
end of the file, and therefore ffmpeg fails to determine what to do
when piped input.

However, say I know all the details of the codec and container, can I
specify them on the command line so that the pipe method would work?
Say I created the file myself, and or have ffprobed the file
previously.

For instance:

cat file.mp4 | ffmpeg -f xyz -pix_fmt rgb24 ... -i - towhatever.ext