My last few shows have been live streamed, but recorded locally for the client. Every time, the A/V sync is perfect at the beginning, but gets further and further out of sync as the show goes on. Any ideas?

Recorder Settings:
Size: 1920x1080 (same as preset)
Frame Rate: 29.97p (same as preset)
Bit Rate: 8Mbps
Profile: H264Baseline
Use Hardware Encoder: On
Fault Tolerant: On
Audio Bit Rate: 128Kbps

I had the same issue a few days ago during a live stream. (Running 23.0.0.66)

I had ticked the "Fault Tolerant" option for MP4 and was also recording vMix AVI. (On previous productions, I had NOT ticked that option) I didn't know there was an issue until a few minutes into the broadcast when someone reported the stream was out of sync. (I stream SRT out of vMix to an SRT Decoder.) However, since I didn't know what was causing the sync issue, I just kept going. Then, suddenly I ran out of storage space, the recordings stopped, and then people started reporting the stream was finally in sync.

I cleared up space and began recording again. The sync issue returned, so, figuring the recording was the cause of the sync issue, I just stopped recording.

Afterward, I checked and the mp4 recording is out of sync. The vMix AVI was in sync (I checked it after converting to ProRes LT).

If "Fault Tolerant mode is not supported by many players and editors," should maybe have a warning that it "...is not supported by many players and editors and could also cause sync issues."?

Please advise.

Christopher

I have been struggling with this issue for months. vMix is running on a new, dedicated HP Z4 G4 workstation with a 10 core CPU, 16 GB RAM, and Nvidia P2200 GPU. CPU, GPU, RAM. All are lightly loaded during production. We use 3-PTZOptics NDI cameras and 1 Mevo Start NDI. All are on the same lightly loaded network switch. Audio input is a feed from the house sound mixer. Performance settings have been set in Windows 10 and vMix per recommendations and we're not using Fault Tolerant mode. Drivers have been updated to the latest. We stream to Vimeo and record locally. Sync drift is not a function of streaming. It happens whether we are streaming or not. Other than Chrome to manage the Vimeo stream control panel, we are not running any other applications on this PC.

I find sync drifts over time. It tends to be about 2 frames an hour but is not linear and can be more or less. I have done repeated testing using bouncing ball and live video to determine the best offset. Seems 165ms is about right. It's very hard to get consistent results from one test to the next. My standard operation procedure is to restart vMix shortly before going live to reset the sync error and then closely monitor sync making adjustments as best I can while live.

I'm looking for clues as to what's causing our sync drift.

I have ProPresenter running on a separate workstation. Video from ProPresenter is fed to vMix via NDI while audio is via house mixer. There does not seem to be any drift in audio sync. Today vMix had been running for about 2 hours. Sync from PTZOptics cameras was off by about 6 frames. Sync from ProPresenter was spot on. After restarting vMix, sync from the PTZOptics cameras was fine as was sync from ProPresenter.

Changing to SDI instead of NDI is not trivial. Others seem to make this setup work so I'm not ready yet to give up on NDI.