MediaRecorder for what reason can Audio and Video be out of sync?

Question

JavaScript

Hello. The problem is the following.

There is a video recorder in the application:
- Recording is carried out through MediaRecorder, chunks of 1 second are sent via web sockets to the back, there they are glued into 1 file.
- 3 modes:
1) webcam recording (getUserMedia with required attributes and stream to MediaRecorder), nothing unusual
2) screen recording (getDisplayMedia and stream to MediaRecorder)
3) screen + webcam: get 2 Webcam and Screen streams and broadcast them to the canvas, the canvas's stream goes to the MediaRecorder.

Problem:
For some users, the audio is recorded with a certain shift, and it turns out that the picture of the video and the audio track are out of sync. I can’t reproduce it myself (on a poppy with M1), there are similar cases both on Windows and on top-end poppies. Has anyone come across? What could be the reason?

Answer 1

An example from DirectShow. It can be seen that the audiorenderer monitors the synchronization (if the videorenderer does not have time to draw, then the sound continues to go at normal speed). The timestamps themselves are present in the source stream. While the suspicion that the shift occurred at the time of recording.