On Tue, Aug 11, 2020 at 11:54 PM Shaun Procter <[email protected]> wrote:
> > On 12 Aug 2020, at 9:01 am, Rich Andrews <[email protected]> > wrote: > > > > Is there any trick to slow down ffmpeg on a simple stream mapping? > > > > Stream mapping: > > Stream #0:0 -> #0:0 (pcm_s16le (native) -> pcm_s16le (native)) > > > > Given an input file that is looped and output with a command such as: > > > > ffmpeg-4.2.1-armhf-static/ffmpeg -y -t 200 -stream_loop -1 -i > HoldMusic.wav > > -map 0:a:0 -f wav output.wav > > > > ffmpeg can move the data really quickly! > > > > bitrate=1411.2kbits/s speed= 262x > > > > Any way to get that speed down to ~1x? My purpose is that ffmpeg is > being > > used as a child subprocess and I would like to be able to test its > behavior > > in-situ. There is a lot of timing in my application between fork and > join > > and having ffmpeg be slow would be really helpful. > > > > Push comes to shove, I'll just use another program to more slowly copy, > but > > that wouldn't be as good as using ffmpeg itself since it has a host of > > behaviors as a child process regarding signaling and return codes. Come > to > > think of it, since I built ffmpeg, maybe I can just build a variant that > > sleeps frequently? > > > > You can use the -re flag like this, > > ffmpeg-4.2.1-armhf-static/ffmpeg -re -y -t 200 -stream_loop -1 -I > HoldMusic.wav -map 0:a:0 -f wav output.wav > > “The FFmpeg's "-re" flag means to "Read input at native frame rate. Mainly > used to simulate a grab device." i.e. if you wanted to stream a video file, > then you would want to use this, otherwise it might stream it too fast (it > attempts to stream at line speed by default). My guess is you typically > don't want to use this flag when streaming from a live device, ever.” - > https://trac.ffmpeg.org/wiki/StreamingGuide > > Hope that helps. > > Shaun > > I feel silly for having looked at that very switch and didn't bother trying it thinking that the input file doesn't have a framerate. '-re' works perfectly. Thank you for the perfect solution! _______________________________________________ ffmpeg-user mailing list [email protected] https://ffmpeg.org/mailman/listinfo/ffmpeg-user To unsubscribe, visit link above, or email [email protected] with subject "unsubscribe".
