Question / Help Blackmagic Intensity Pro 4k audio drifting out of sync

[TheAstropath]

Hi,

I'm using a Blackmagic Intensity Pro 4K capture card and am having some difficulty getting audio synced up properly. Sometimes when I start OBS and do a recording the audio starts synced up (Audio and video are lined up properly), and then quickly drift out of sync (Audio ends up about a second behind the video after about a minute, and gets worse as time goes on). Other times the audio starts at least a second out of sync with the video and presumably continues to drift away over time (It's a bit harder to judge this case, since it was never in sync to begin with).

Sometimes I can bring the audio back into sync temporarily by disabling and re-enabling the "Blackmagic Device" capture, or by changing the input to a different resolution and back, although this doesn't seem to work consistently.

I'm using OBS Studio 18.0.1 64 bit, and tried two versions of the Blackmagic Desktop Video drivers (The latest version, 10.8.5, and the previous version 10.8.4)

I captured the same video source through the Blackmagic Media Express software and didn't encounter any issues with the sound being out of sync or drifting at all. I also tried AmarecTv and it didn't seem to have any issues. Is there any particular setting I need to be using in OBS to prevent the drift and out of sync audio? Any particular version of the Blackmagic drivers I should be trying?

Log file Attached

-Astro

 

[c3r1c3]

Is buffering enabled on the BMD source?

Also I don't see any BMD sources, only DirectShow sources. Are you using the BMD source-type for your BMD device? If not, please switch to that ASAP.

Lastly I see you using Voicemeter. If you can use the new audio routing abilities in OBS 18.0.1 without using Voicemeter (or lessen your dependence on it), please consider modifying your setup to take advantage of it.

 

[TheAstropath]

I tried buffering on and off to see if it made any difference, and while buffering did help somewhat, it was still out of sync.

The source called "Blackmagic Device" was created through the Add>Blackmagic Device menu option, although I see it shows as a decklink-input.

Re: Voicemeeter - I'm actually mostly using that for non-OBS related purposes. The mic doesn't go out of sync with my webcam video though, only the Blackmagic audio (Not running through Voicemeeter) goes out of sync with the Blackmagic video.

Looking at the log again, I'm realizing that I don't think I've checked to see if the audio desyncs if I don't have the Aspect Ratio filter applied to the capture card, although that feels like it would be an unlikely issue.

 

[Suslik V]

Probably, you posted wrong log-file, because the Blackmagic Device source didn't initialized during all this recording attempts.

 

[TheAstropath]

OK, just to be sure, I quickly did another test here to get a new log file, definitely using the Blackmagic Device source that I had created (Still showing as decklink-input). I've attached the new log file. I see in both files a line that says "Blackmagic Device: Starting capture...", although it is outside of the start/stop recording point. In the new log file I started and stopped recording twice. I am definitely capturing from the blackmagic card in this file.

 

[Suslik V]

And still have sync issues in this recording?

 

[TheAstropath]

Yes, still having sync issues. As far as I'm aware. I didn't change any settings between generating the log last night and this morning.

 

[Suslik V]

How you getting audio from the device (USB bus, Line-in, other...)? Sure that the bus not overloaded? Post your Blackmagic Device source settings, please (Device, Mode, Pixel Format, Use Buffering settings).

 

[TheAstropath]

The Intensity Pro 4K is an internal PCI-e card, and the audio is being captured through that, along with the video. I only have 2 PCIe devices in my computer, my graphics card and the Intensity Pro 4K. I checked the manual for my motherboard to ensure I had the capture card in the most appropriate slot to work alongside the graphics card.

I've tried input via both HDMI (720p60) and composite (NTSC) and experienced the same issue, both with and without the Use Buffering option.

In terms of colour mode, I know there was 8-Bit BGRA and 8-bit YUV. HDMI only works on one (I believe BGRA) and composite only works on the other (I believe YUV). I can verify which one is which later today.

 

[Suslik V]

Blackmagic Media Express and AmarecTv captures sound via Voicemeeter virtual device?

 

[TheAstropath]

No, both directly from the capture card as well.

That being said, I think I might see where you're going with this (Or at least, something to rule out outside influences). I can try doing a recording in OBS without any other sources except the video and audio from the Blackmagic card to see if I get any delay that way.

 

[Suslik V]

At least, I'm holding you at top for about two days. If someone else has the same problem with Intensity Pro 4K then you have a bit more chance to be noticed and be helped, I think. If not - probably your issue unique and nothing to do with it.

 

[TheAstropath]

Yeah, thanks!

I tried the Blackmagic card on it's own and still had audio desync. A friend suggested ensuring all of my audio was being sampled at 48 kHz, since that's what's coming off the HDMI, and everything else was being sampled at 44.1 kHz, but that still didn't help either.

Honestly, I think I'm at the point where I'm just going to return the card and buy something else that has greater reports of success. Sorry anyone else who happens across this thread in the future! No resolution to this problem!

 

[Suslik V]

Actually, the Blackmagic has the lowest claim reports from all other manufacturers on this forum (maybe expensive device or good quality). So, try something else before throw your money. Also, try to contact the manufacturer support.

Edit: One more thing, can you make test scene where Blackmagic device initializes first of all (maybe new Scene Collection with only Blackmagic Device source in it).

 

[Fenrir]

I've been investigating a similar issue, but mine does not drift that quickly. Over 4-5+ hours, the audio will desync about 100-200ms. You say it happens pretty much right away and desyncs?

 

[cpond]

I apologize for bringing up an old thread, but I have recently noticed a similar issue to what Fenrir was investigating in 21.0.1 (on an HP with i5, using quicksync, and a Decklink Duo card), but for streaming not recording.
I will post logs ASAP (machine is in transit) but in the meantime I wanted to ask if this was still known behavior in 21.0.1?

Description of issue:
Streaming multiple sporting events at 1080p2997 over RTMP.
Over 3 hour broadcast lip sync is fine through the end of the broadcast.
2 hours between events (potential for muted/no audio on the line, possibly a factor?)
When 2nd event starts Lip Sync is off by an appreciable amount (I would guess 200-500ms but I'm eyeballing it)
Only fix is to restart OBS (stopping starting sources/streams does not effect.

Problem persists whether stream is started or stopped (leads me to believe its a problem on the intake of video/audio).
Resulting stream has been tested as out of sync in OBS, VLC, FFMPEG (outputting to a decklink card) and FFPLAY.

Again, logs to come ASAP....

Thanks,
-chris