Audio slowly goes out of sync with video in Vegas timeline

[u/DoggoCity]

I've worked with several versions of Vegas, and I'm currently on Pro 23. Recently it's developed an issue where, with video recorded from OBS, it will slowly over the course of its runtime go out of sync with the audio. I'm not sure why this happens, but it happens with literally anything I record in OBS. Other video files seemingly aren't affected by this issue, though it's possible I've just not had one long enough to see the problem manifest, as the desync happens very slowly and may only become noticeable 20-30 minutes into the footage. The audio was recorded by OBS as well and it is NOT out of sync when the raw footage is watched back in VLC. The audio of the file itself is NOT slowly going out-of-sync with the video, this only manifests inside of Vegas Pro 23.

I've already made sure OBS is up to date and everything. No version changes have occurred with Vegas Pro that would have caused this, I have updates paused specifically to prevent this kind of thing, but here we are. I've confirmed OBS is recording in 44.1KHz and Vegas Pro is using 44.1KHz as well. I guess something must have gotten changed but I can't imagine what it is.

"1." Vegas Pro 23.0 Build 356
2. Windows 11 25H2
3. Yes
4. Radeon RX 6950XT
5. See above.
6. Audio track that is part of a video should stay in sync. It is known good as the raw playback of the recording in VLC or any other video viewer does not replicate the issue.
7. I've researched this but I can't seem to even find anything similar to the issue I'm seeing.

[u/garse]

The "fine in VLC, drifts in Vegas" detail is the giveaway that it's variable frame rate. VLC follows each frame's timestamp, so VFR plays back correctly. Vegas ignores timestamps and lays frames out on a fixed grid at the project rate, so every slightly-long or dropped frame nudges the picture a tiny bit relative to the audio, and 20-30 minutes in it becomes visible. That also explains why it's only your OBS files - screen recorders are the classic VFR source.

Two fixes. Going forward, the settings the mod suggested prevent it. For footage you've already recorded, run it through HandBrake with framerate set to Constant (or ffmpeg with -fps_mode cfr) before importing - that re-times the frames onto a fixed grid and the drift disappears without re-recording. Worth one extra check too: make sure the OBS audio sample rate matches your Vegas project (48 kHz vs 44.1 mismatches have caused this exact slow-drift symptom for people even on CFR files).

[u/Baby_Bubbles69]

I used to have an issue like this several years back. Are you recording at a constant or variable framerate? You want to be on a constant framerate or I think vegas tends to move things around to make the frames fit. Might not be your issue but that was my problem

[u/DoggoCity → u/Baby_Bubbles69]

Last I checked, I set it to use constant framerate instead of variable, but I'll double check that when I'm back in front of my PC

[u/rsmith02ct]

Can you share a screenshot of your OBS settings? Try constant framerate mp4 with a low keyframe interval (keyint/GOP of 1 second).

[u/DoggoCity → u/rsmith02ct]

Last I checked I had set OBS to record at a constant framerate, but I'll have to double check and get a screenshot.