[FFmpeg-user] Audio/video stream are out of sync?

[christina zou]

Thanks for the reply. I am using a little wifi module on my Pi Zero and
want to send the minimum amount of data so I don't experience buffering and
frame drops. So I am using 10 fps. I don't think my setup could handle
25-30 fps?

Should I be adding in a param related to keyframes, though?

It is indeed my audio that drifted out of sync after 3 minutes, so I will
try adjusting the bitrate back to 32K.

On Wed, Feb 8, 2017 at 11:31 PM, Erik Dobberkau <erik.dobberkau at gmail.com>
wrote:

> Am Donnerstag, 9. Februar 2017 schrieb christina zou :
>
> > I've made some progress thanks to advice from the IRC channel. I
> increased
> > my pipe max buffer size as high as I could:
> >
> > sysctl fs.pipe-max-size=1048576
> >
> > I also lowered my video resolution and bitrate.
> >
> > Now, with the below command I've managed 3 minutes of fully synced
> > audio/video livestream to Youtube from my Pi Zero. At the 3 minute mark,
> > there's a slight desync, and the audio goes about 0.5s ahead of the
> video.
> >
> > That's my next question. I don't mind if there's a stutter every 3
> minutes,
> > but I need the A/V sync to recover after that. So if I lose a few audio
> > frames, I need the video to catch up (or audio to slow down). Any
> > suggestions about how to do this (either ffmpeg param, or script)?
> >
> > Here's my current command:
> >
> > sysctl fs.pipe-max-size=1048576
> >
> > *sudo rm temp_audio.v*
> >
> > *sudo rm temp_video.h264*
> >
> > *mkfifo temp_audio.v*
> >
> > *mkfifo temp_video.h264*
> >
> > *arecord -Dmic_sv -c2 -r48000 -fS32_LE -twav temp_audio.v & \*
> >
> > *raspivid *-w *640* -h *480** -fps 10 -v -b 1000000 -o temp_video.h264
> -t 0
> > & \*
> >
> > ~/special/ffmpeg/ffmpeg* \*
> >
> > *    -framerate 10 \*
> >
> > *    -i temp_video.h264 \*
> >
> > *    -i temp_audio.v \*
> >
> > *    -ab 24k \*
> >
> > *    -c:v copy \*
> >
> > *    -c:a aac \*
> >
> > *    -report \*
> >
> > *    -f flv **rtmp://209.85.230.23/live2/KEY*
> >
> > On Wed, Feb 8, 2017 at 3:50 PM, christina zou <zou.christina at gmail.com
> > <javascript:;>>
> > wrote:
> >
> > > Carl,
> > >
> > > I spent a lot of time trying to use ffmpeg alone (alsa/v4l2), but it
> > > produces extreme stuttering on the audio track. Using my approach of
> > > writing to named pipes and sending those into ffmpeg, I add a bit of
> > > latency but ensure that there's no loss of frames. This was the
> approach
> > > suggested to me by the ffmpeg IRC channel. I'm on a Pi Zero (single
> > core),
> > > by the way.
> > >
> > > Is there any way to align the two input streams' timestamps, if they
> are
> > > both being read from named pipes?
> > >
> > > Here is my full console output: http://pastebin.com/phmiphaL
> > >
> > > Thanks,
> > > Christina
> > >
> > >
> > >
> > > On Wed, Feb 8, 2017 at 3:02 PM, Carl Eugen Hoyos <ceffmpeg at gmail.com
> > <javascript:;>>
> > > wrote:
> > >
> > >> 2017-02-08 22:57 GMT+01:00 christina zou <zou.christina at gmail.com
> > <javascript:;>>:
> > >>
> > >> > *arecord -Dmic_sv -c2 -r48000 -fS32_LE -twav temp_audio.v & \*
> > >>
> > >> Why?
> > >> (See below)
> > >>
> > >> > *raspivid -fps 10 -v -b 3000000 -o temp_video.h264 -t 0 & \*
> > >>
> > >> Is this not possible with ffmpeg alone?
> > >>
> > >> > ~/special/ffmpeg/ffmpeg* \*
> > >> > *    -framerate 10 \*
> > >> > *    -re \*
> > >> > *    -i temp_video.h264 \*
> > >> > *    -i temp_audio.v \*
> > >>
> > >> (Complete, uncut console output missing.)
> > >> How are these two input streams supposed to be synced?
> > >>
> > >> Normally, you would use (for example) alsa and v4l2 input
> > >> and hope that the two drivers both provide wallclock timestamps.
> > >>
> > >> Carl Eugen
> >
>
> My suspicion is the transcoder the stream is being fed to doesn't cope well
> with the framerate. In my experience it's most stable when using either 25
> or 30fps with a keyframe interval of 50 or 60 frames maximum. Also best to
> use standard bitrates, especially with audio, to avoid drifting.
>
> Erik
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