Video and audio from different sources, out of sync

[SteveBlakemore]

Hi,
I'm using OBS to record video of people talking, using two PTZ cameras over rtsp. Sound is coming in to the same laptop with a Rode Wireless Go II receiver, connected via USB. There is one or sometimes two lapel mics connected wirelessly to the receiver. The video records in good quality, so does the sound, but the problem is they are not together! The video is several seconds behind the audio, so I have the job later of aligning them and this is difficult to get right.
Does anyone have any suggestions to get the sound and video recorded together from the start?
Thanks in advance,
Steve

 

[AaronD]

RTSP is designed to survive the open internet, with packets being dropped all over the place and resent. So it has a LOT of buffering built into it, so those resent packets can slot in before they're needed. That's where your delay is coming from.

Do the cameras support NDI? Or something else that is designed to be almost instant, but requires a solid dedicated connection to do it? (running that across the internet would kill it)
Or can you run a dedicated video cable from each one to the PC, and use a video capture device? Not the $20 USB garbage, but actual quality: $100 per channel USB, or PCIe.

Once you get it down to a 1/2-second or less, you can use the Sync Delay in the Advanced Audio Properties to finish the job by trial and error. (the Monitor doesn't reflect this, which makes the process kind-of annoying, but you only have to do it once as long as everything else stays constant) Bigger number makes the audio come later. A small negative number works too, to make it earlier, by eating into the small buffer that OBS has, with the risk of making the buffer too small and having the audio "break up".

 

[SteveBlakemore]

Hi,
The cameras do support NDI, and I remember trying it, but can't remember why I settled on rtsp! I'll try NDI again. Thanks for the advice, I'll give it a go and come back to this thread in a couple of days.
Steve