<p>This is on linux with pulseaudio. I need to record a video with a rather bare-bones recorder that runs in chrome. I decided to fake a camera and a mic so that I can edit the video then use ffmpeg to send the video to a dummy camera created with v4l2loopback and set the chrome input in pavucontrol. This s what I have:</p>

<pre><code>ffmpeg -re -i ~/xxx.mp4 -map 0:v -f v4l2 /dev/video2 -f pulse "alsa_output.pci-0000_00_1f.3.analog-stereo.monitor"
</code></pre>

<p>where /dev/video2 is the loopback camera. This seems to work fine, but the audio lags the video by a few seconds. I verified that they are very much in sync by playing the mp4 normally. How do I fix this?</p>

CC BY-SA 4.0
2020-04-06T18:15:24.630Z
Is it a consistent lag or does it change over time?
llogan
CC BY-SA 4.0
2020-04-06T21:43:23.457Z
The lag seems to be roughly the same after 22 minutes of streaming.
melisgl
<ffmpeg><linux>
ffmpeg fake camera and mic out of sync
melisgl
# ffmpeg fake camera and mic out of sync

(Asked by: username_0 on 2020-04-06)

This is on linux with pulseaudio. I need to record a video with a rather bare-bones recorder that runs in chrome. I decided to fake a camera and a mic so that I can edit the video then use ffmpeg to send the video to a dummy camera created with v4l2loopback and set the chrome input in pavucontrol. This s what I have:
ffmpeg -re -i ~/xxx.mp4 -map 0:v -f v4l2 /dev/video2 -f pulse "alsa_output.pci-0000_00_1f.3.analog-stereo.monitor"

where /dev/video2 is the loopback camera. This seems to work fine, but the audio lags the video by a few seconds. I verified that they are very much in sync by playing the mp4 normally. How do I fix this?

**Tags:** ffmpeg, linux

> **Comments:**
> **username_1**: Is it a consistent lag or does it change over time?  
> **username_0**: The lag seems to be roughly the same after 22 minutes of streaming.  

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## 0 answers

