[FFmpeg-devel] make ffmpeg transcode a growing file

Rodney Baker rodney.baker
Sun Mar 8 06:10:52 CET 2009

On Sun, 8 Mar 2009 12:20:04 Michael Brennan wrote:
> Hello,
> I would like to be able to transcode an mpeg2 file at the same time it is
> being recorded to disk. I would like to start the recording of the mpeg2 to
> disk, and then about 30 seconds later begin transcoding the mpeg2 to mp4
> file output. I see that ffmpeg currently will transcode a growing file, but
> will often catch up to the end of the file before the recording is
> finished. Ffmpeg will then quit normally and the resulting output file will
> be fine, although it will not be as long as the mpeg2 that is still
> recording.

I think this belongs on ffmpeg-user rather than ffmpeg-devel. Nevertheless, I 
do this quite often between mplayer and ffmpeg for audio files that are 
streamed off the web, by directing mplayer's output to a named pipe, then 
telling ffmpeg to read from the named pipe. If there is a pause in mplayer's 
output, there is a corresponding pause in ffmpeg's input but it does not quit 
until mplayer closes the pipe.

If you need to keep the original file you could use tee to write it to both a 
physical file and a named pipe.

There may be other preferred ways to do this but this method works for me.

Anyway, I suggest we move this discussion to the -user mailing list...


Rodney Baker VK5ZTV
rodney.baker at iinet.net.au

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