How can I pipe output of ffmpeg to ffplay?

Question

How can I pipe the output of ffmpeg to ffplay?

At the moment I use a workaround in bash :

mkfifo spam
(ffplay spam 2> /dev/null &) ; capture /dev/stdout | ffmpeg -i - spam

Answer 1

I do not know if it is ffmpeg that cannot output its data to stdout, or ffplay that cannot take its input from stdin.

If it is ffmpeg that cannot output its data to stdout:

capture /dev/stdout | ffmpeg -i - >(ffplay 2> /dev/null)

(You migth need to add a - argument to ffplay so it takes its input from stdin.)

If it is ffplay that cannot take its input from stdin:

ffplay <(capture /dev/stdout | ffmpeg -i -) 2> /dev/null

For more informations about the <(command) and >(command) construct, see the Process Substitution section of the bash manual.

Answer 2

looks like normal pipes work (at least in windows):

ffmpeg -i sintel.mpg -pix_fmt yuv420p -f rawvideo - | ffplay -f rawvideo -pix_fmt yuv420p -s 720x480 -

haven't tried it with more complicated input/output though...

ffmpeg -f dshow -i video=screen-capture-recorder -pix_fmt yuv420p -f mpegts - | ffplay -analyzeduration 10 -f mpegts -

is slightly faster startup

Answer 3

ffmpeg supports piping operations. See that section of the documentation here.

I don't know how ffplay works, but to pipe the output of ffmpeg to standard output, you can add the pipe command to the end of the ffmpeg command. Example:

ffmpeg -i input.flv pipe:1 | ffplay -i -

Answer 4

ffmpeg -i input.avi <options> -f matroska - | ffplay -

will work; you need to set a container format for the output. This is normally set with ffmpeg looking at the extension you give the output, but here you have to set it manually with -f. I recommend matroska (MKV) because it can contain almost any video, so whatever you're transcoding it to should work perfectly well.

Note that if you are using Ubuntu 12.04, ffmpeg has been replaced by the libav fork, and you should use avconv and avplay instead; the syntax is otherwise identical. There is a sort-of ffmpeg there, but it's crippled by design.