How to adjust audio latency?

[Botspot]

My application involves voice narration and a video feed of the webcam, inside a small mplayer window on-screen to be captured along with everything else. The problem is that the webcam previewer has a bit of lag, causing the audio to play about 0.5s ahead of the video.

Is there a easily known way to tell ffmpeg to add latency to the audio? I would rather not do this with post-processing.

[soreau]

Are you using gstreamer for the webcam preview as mentioned in the wiki?

[Botspot]

Are you using gstreamer for the webcam preview as mentioned in the wiki?

No, that seemed to perform very poorly, and the window could not be resized or moved. I was using this:

mplayer -vo xv tv:// -tv driver=v4l2:device=/dev/video0:width=640:height=480:fps=30

Edit: mplayer appears to be running under x11. That may be contributing to the latency.

[soreau]

Maybe try something like mpv --gpu-context=wayland --hwdec=vaapi.

[Botspot]

I've asked for help here: https://forums.raspberrypi.com/viewtopic.php?t=371908

[soreau]

For what it's worth, you should be able to resize the gst-launch window with the wayfire resize binding, the default binding is here. (Super+Right Click Drag)

[Botspot]

mplayer appears to be running under x11. That may be contributing to the latency.

It was, and also made the entire recording lag. This works extremely well.

mpv av://v4l2:/dev/video0 --profile=low-latency --untimed=yes --video-latency-hacks=yes --wayland-disable-vsync=yes --video-sync=display-desync

I would still like to delay the audio just slightly, so not closing this issue quite yet, but I suggest you add this to the wiki in case it helps others.

[Botspot]

Is there a way to pass arbitrary flags to ffmpeg? I think the -itoffset flag does what I want.

Things I've tried:

yes | wf-recorder -a -f /tmp/video.mkv -c libx264 -p preset=ultrafast -r 30 -F=-itsoffset=5
#fails
yes | wf-recorder -a -f /tmp/video.mkv -c libx264 -p preset=ultrafast -r 30 -P=-itsoffset=5
#has no effect

[soreau]

I think you might want --codec-param="-itsoffset=5"

[Botspot]

I think you might want --codec-param="-itsoffset=5"

No change. For ffmpeg, -itsoffset must be specified before the input you want to offset, in case that detail becomes important.