All,

I'm currently facing an issue I can't explain. I'm ingesting HD-SDI (720p59.9) with embedded Audio using a BM Decklink Duo 2 into vMix (720p59.9 project) . The audio is perfectly in sync with the video (mixing console video out is delayed to compensate). I can verify this with a BM Hyperdeck which is recording the incoming signal (both devices are connected to a SDI Matrix).

Even without any processing on the vMix (SDI Input to PGM; PGM to the second Decklink channel) I see an Audio Delay in the output SDI (2.5-3 frames).

So basically a perfectly locked/synced SDI signal comes in ... but an SDI signal with audio delay leaves the machine.

Any idea how to fix this?

In other posts I read about negative audio delay (e.g. vMix adds audio delay by default to compensate for delayed video). In my case however this is not neccessary and I have no idea how to fix this. Even the "negative Audio delay" mentioned in some posts does not change anything here (does it work at all? E.g. compensating the default delay that vMix add?).

Any hints/help appreciated.

CU,

Udo

Hi there,

I'm also having the same issue with our setup:

• vMix 25 on Windows 10 64-bit
  BMD Intensity Shuttle USB 3 device using Blackmagic Desktop Video 12.2.2 software
  1080i50 video & audio feed coming from ATEM Production Studio 4K over HDMI to the BMD capture card.

The issue is that the audio delay is inconsistent. Like I added -85ms to get it in sync and then the next time I did a video stream it was not longer in sync.

Now I believe the issue is actually with Blackmagic's drivers on Windows 10, because I've also struggled with this kind of issue when using OBS also on another PC that also has a Blackmagic card: Mini Recorder 4K.

I don't know what Blackmagic's Media Express software is doing differently, but so far it has always been in sync when doing recordings with it.

I've now started a support ticket with vMix about this and the very first thing they pointed out was that my Intensity Shuttle USB 3 device isn't supported by vMix. So I'll go and swap that out with our other PC's Blackmagic Mini Recorder 4K, but I doubt that it will fix anything.

Okay, so it turned out that my issue was that the way that I analyzed whether my audio & video was in sync, by inspecting the saved MP4 recordings with DaVinci Resolve 17 was completely flawed. When I set vMix to record to AVI (YUV Uncompressed), the audio & video was showing as being in sync in Resolve.
Using VLC at a 0.25 playback speed showed that all my MP4 recordings from vMix were actually in sync, except when I used FFMPEG output (MP4 NVENC AAC codec) during testing.

I have also swapped my Intensity Shuttle USB 3 (used HDMI input) for the Mini Recorder 4K (now using SDI input), however I believe my issue was just that I analyzed the audio sync with flawed software or wrong settings in Resolve. Some of my issues might have also been resolved by upgrading to Blackmagic Desktop Video 12.2.2 software.

The support engineer from vMix also encouraged me to test the audio sync by using the vMix direct output to an external monitor & audio, without either Recording to file or Streaming to an online service, which also allowed me to check if things are roughly in sync, however I still need to inspect a recorded file at like 1/4x speed to accurately verify if things are in sync.

The process that I use for my sync testing is to use the audio/video sync tests from PhotoJoseph as he's recommending to use them, except that I'm now using VLC at 0.25 playback speed instead of an NLE.

Hello Pada,
So, this thread is the closest to what I am experiencing right now. The main issue is out of sync video/audio. The funny thing is everything starts off in sync and then after a strange audio distortion the recording and stream go out of sync about 21 frames. The video ends up ahead of the audio. I have to add the video delay in Vmix to sync it up again.

As our session continues, we have to readjust the video delay usually by reducing the frame delay. But it's never the same once the out-of-sync starts.

Our present setup is:
1. Omen PC with Nividia 2080RTX - gaming system but bought it for our streaming/recording because of video capabilities.
2. BlackMagic 4k Studio cam/BlackMagic HD Studio Cam output to ATEM Studio HD which is PGM out to BM Web Presenter HD
3. Behringer QX2442USB XENYX which is output via XLR to ATEM

The web presenter is output via USB to the USB-C on the nividia.

I control volume clipping using ATEM Control software or, if needed, the audio slider in Vmix. As far as audio, I believe from the Vmix tutorials all the boxes I need to have checked are. So, not sure what is causing the issue.

Anyway, any ideas will be helpful.