Growing Audio Delay

First system info. Wirecast Studio 14.1.2 running on a Mac Mini 2018 i7 3.2GHz 6- core, 32GB RAM. 500GB SSD. Video capture device is BMD UltraStudio Express (with Apple TB2-TB3 adapter) Desktop Video Driver version 11.7. The Mini is running Mac OS 10.15.7 Catalina. 

Very simple setup. 1080i29.97 Video with embedded audio from a fiber receiver is routed to the UltraStudio. Wirecast takes that feed and encodes to YouTube using unmodified YouTube 1080p30 x264 Recommended (4.5 Mbps) encoding profile. No overlays, no chroma key just a straight re-transmit. The only other shots are a holding slate with a looping audio clip, a "We are having technical difficulties" slate and a "Thank You for Joining Us" slate. Like I said very simple.


Issue: Three hour live stream. At zero minutes the A/V sync from the UlraStudio is perfect. Hour 2 audio is delayed .1 seconds or so noticeable. Hour three audio is delayed .3 seconds or so, very noticeable. It's not just the stream to YouTube that is delayed. The Wirecast program monitor is also out of sync. 

This was never seen in any of our dozens of previous streams (most of those were 720p, however). Nor did we see any issues during any of our tests leading up to this latest event (none of the tests went the full three hours, unfortunately.)

Now, to add to the scenario we had an *identical* Mac Mini running as a backup. It had the exact same issue.  

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  • Eric geppner said:
    First system info. Wirecast Studio 14.1.2

     Please update to 14.2.1 and test in a new document. Updates include fixes and some may have been around sync drift. 

    Eric geppner said:
    Desktop Video Driver version 11.7

     The latest driver compatible with Catalina is 12.1 so updating that may impact this as well.

    You may want to change the incoming timestamps but that's used to address these issues.



    What are Timestreamps

    Also see Page 132 of the User Guide

  • I ran the updates so now Wirecast 14.2.1 and BMD driver 12.1.

    I setup the same test.

    I created a new document.

    Same video (1080i29.97) in on the UltraStudio.

    Same YouTube 1080p30 x264 (4.5Mbps) encoding profile.  

    I left Timestamps on Provided by Source (change one thing at a time).

    I let it run for about two hours and checked back to find the A/V sync was out.

    I discovered that if I stop the stream but leave YouTube running and restart the stream the A/V sync goes back to perfect. (I have Auto-start and Auto-stop turned off.)

    For the next test I will try Timestamps: Generated by Wirecast and see what we get.

    But that's for Monday. 

    Have a nice weekend.

  • Make sure to check the audio section of the card and the stream setting. Don't mix 44.1 and 48KHz

  • Eric geppner said:
    For the next test I will try Timestamps: Generated by Wirecast and see what we get.

     Thanks for doing that. And as Jens notes, Audio Sample Rate is important as well. Please note that for your source.

  • Yeah, everything is set to 48kHz.

    It looks like Timestamps: Generated by Wirecast is the solution. I've got a test stream running right now that is still in sync after 2+ hours. I'll see what it looks like at 4+ hours and if it's, as I expect, still good we can mark this as Solved. Thanks CraigS.

  • Eric geppner said:
    It looks like Timestamps: Generated by Wirecast is the solution.

     Good to hear. We added that feature because we found the variance in timestamp accuracy between input devices.

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