Audio/Video Desync Over Time

raisinbrands

New Member
Hello!

Firstly, thank you for taking the time to read through this problem I've been experiencing.

Recently, our streams have begun to lose audio/video sync over time - initially, our sync was fine at first, but then about an hour and a half into our stream, the audio/video would desync by about half a second, but noticeable enough. We have also seen some frames seemingly speed up/slow down during more production heavy portions of the service.

We are using a multi-camera system by Blackmagic, and the output is sent to our streaming iMac via SDI to a Blackmagic capture device (UltraStudio HD Mini). Audio is embedded in the capture device. We stream at 1920x1080p at 30 fps, and our settings are as follows:

  • Encoder: x264
  • Rate Control: CBR with a bitrate of 4500 Kbps
  • Keyframe Interval is at 2
  • CPU Usage Preset is set to very fast, and the profile/tune are set to None.
  • Audio sample rates are at 48 kHz for all of our inputs (we have audio being sent to us via a Wing console, which is set to 48 kHz)
  • Downscale Filter is set to bicubic, 16 samples
  • All firmware is up to date: OBS is at v.27.1.3, and the capture device is at its' most updated firmware version
  • The iMac used for streaming is a 2019 iMac that is currently using Big Sur 11.6.1
  • Color format is at NV12, Color space is set to 709
  • All cameras have the same settings (which they need to in order for me to receive signal to switch to them): a framerate of 60fps + a shutter speed of 1/60 s

What we're seeing is that, even with a local recording and looking at playback, there is a desync occurring, which may (or may not) indicate that streaming through our multi stream service is not the issue. I've been leaning towards an OBS setting that maybe needs more adjustment, but I'd like more input/advice from this community.

If there is a way for any of you to help identify + indicate an issue, and maybe work through towards a solution, with our problem, that'd be amazing! Thank you so much for helping us out with this issue.
 
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