Blackmagic Decklink Mini Recorder variable Audio/Video Sync Issue

[aaroncoolidge]

We use a black magic decklink mini recorder to capture the audio and video from our Canon xa35. We use this source in conjunction with others to mix for our live stream and are recordings which we upload to our various accounts later. For the past several months we have had an issue where occasionally there will be a audio video sync issue between the video and the audio. The time delay is not constant it is variable and can change from recording to recording even within the same day. We have found a couple of work arounds that work most of the time, but sometimes despite our best efforts, we still will end up with a sync delay that we have to fix and post. It persist through multiple versions of obs, whether our plugins are enabled or disabled, and through driver updates for the deck link card.

All the guidance and advice that we can find on this issue talk about setting a sink delay in the audio settings between the video and audio, but the delay is not constant and would have to be changed continuously also there is no sink delay in the recordings which are captured in camera directly to the SD card.

 

[khaver]

At my church, we start OBS around 8:30am Sunday morning so an announcements slide show can play in the lobby. Cameras had been set to always be on. When we started recording the sermon around 11:00am the audio and video were always out of sync. We tried setting audio and video delays, but we always had some degree of bad sync. After some experimentation, we have found that if OBS and webcams are running for a long time (hours+) before starting recording, audio/video sync can drift during this time. Closing and reopening OBS just before starting recording would fix this. Because we can't close OBS before recording, we found that having our webcams set to be deactivated when not shown, and just before we start recording, switch to a blank scene so the cameras deactivate, start recording, then fade up to the scene with the cameras, fixed the issue (I created a stinger that delays fading in for a second so the camera reactivation can stabilize before being shown). This seems to "re-set" the sync between audio and cameras so our 45 minute recordings are fine.

Figure out a way to close and reopen OBS before recording or set your capture device to be deactivated when not shown and deactivate and reactivate it just before recording.

 

[aaroncoolidge]

We have found just the opposite, we have to start recording with the camera which has the audio from our sound system without any embellishments for the audio and video to stay in sync. If we're using one of our secondary cameras or our announcements it does not work. Or if we use blank scene, the audio and video will still be out of sync.