Question / Help Problem with Audio and Video sync

[Jocke4s]

We have problem with audio and video sync. Our input is 1080i50 via a UltraStudio Mini Recorder and we currently stream to YT with 1080p25 with bitrate 9,000 Kbps. Earlier we followed the guidelines from YT and used 6,000 Kbps but the video kept lagging behind. It was initially OK but lagged over time. When using 9,000 Kbps and changing the CPU setting are we not experiencing that the video is not lagging.

Today when streaming everything sounded OK on the streaming Mac but on YT we had a audio/video sync issue that was fixed from the beginning. We stopped and restarted the stream a couple of times and also terminated the local harddrive recording without any improvement. In the end we had to add a make up delay in OBS, after a while we had to reduce the make up delay since the initial delay was then too long.

I have three questions:
1) What settings should we change so that we can reduce the bitrate without introducing the unsync between audio and video?
2) What shall the impact of changing the CPU setting be? When chaning it we don't see a image quality change only that we either use so much CPU that nothing is streamed or that we manage to stream but the audio lags more and more over time.
3) What cause the audio and video to be out of sync from the begining?

What type of logs should be provided for analysis? The regular log file is attached.

HW: iMac (Retina 5K, 27-inch 2017), 4,2 GHz, 24 GB, Radeon Pro 8GB
SW: macOS Catalina (10.15.4), OBS 25.0.7

 

[Narcogen]

Increasing audio buffering on a source or interface is often an indication either of CPU overload, or USB bus overload (too many devices trying to use too much bandwidth on a single controller). I don't see encoder or GPU overload in your log, so I suspect USB overload.

08:37:32.786: adding 64 milliseconds of audio buffering, total audio buffering is now 64 milliseconds (source: Blackmagicenhet)
08:49:28.237: adding 21 milliseconds of audio buffering, total audio buffering is now 85 milliseconds (source: Blackmagicenhet)
08:49:28.472: adding 21 milliseconds of audio buffering, total audio buffering is now 106 milliseconds (source: Blackmagicenhet)
08:49:29.842: adding 21 milliseconds of audio buffering, total audio buffering is now 128 milliseconds (source: Blackmagicenhet)
08:49:30.843: adding 21 milliseconds of audio buffering, total audio buffering is now 149 milliseconds (source: Blackmagicenhet)
08:49:31.546: adding 21 milliseconds of audio buffering, total audio buffering is now 170 milliseconds (source: Blackmagicenhet)
08:49:32.132: adding 21 milliseconds of audio buffering, total audio buffering is now 192 milliseconds (source: Blackmagicenhet)
08:49:32.440: adding 21 milliseconds of audio buffering, total audio buffering is now 213 milliseconds (source: Blackmagicenhet)
08:49:33.147: adding 21 milliseconds of audio buffering, total audio buffering is now 234 milliseconds (source: Blackmagicenhet)
08:49:34.278: adding 21 milliseconds of audio buffering, total audio buffering is now 256 milliseconds (source: Blackmagicenhet)
08:51:05.835: adding 21 milliseconds of audio buffering, total audio buffering is now 277 milliseconds (source: Blackmagicenhet)
08:53:13.262: adding 21 milliseconds of audio buffering, total audio buffering is now 298 milliseconds (source: Blackmagicenhet)
08:53:14.052: adding 21 milliseconds of audio buffering, total audio buffering is now 320 milliseconds (source: Blackmagicenhet)
08:53:14.862: adding 21 milliseconds of audio buffering, total audio buffering is now 341 milliseconds (source: Blackmagicenhet)
08:53:17.170: adding 21 milliseconds of audio buffering, total audio buffering is now 362 milliseconds (source: Blackmagicenhet)
08:53:17.569: adding 21 milliseconds of audio buffering, total audio buffering is now 384 milliseconds (source: Blackmagicenhet)
08:53:17.874: adding 21 milliseconds of audio buffering, total audio buffering is now 405 milliseconds (source: Blackmagicenhet)
08:53:18.066: adding 21 milliseconds of audio buffering, total audio buffering is now 426 milliseconds (source: Blackmagicenhet)
08:53:18.574: adding 21 milliseconds of audio buffering, total audio buffering is now 448 milliseconds (source: Blackmagicenhet)
08:53:18.858: adding 21 milliseconds of audio buffering, total audio buffering is now 469 milliseconds (source: Blackmagicenhet)
09:54:38.029: adding 21 milliseconds of audio buffering, total audio buffering is now 490 milliseconds (source: Blackmagicenhet)
09:54:38.230: adding 21 milliseconds of audio buffering, total audio buffering is now 512 milliseconds (source: Blackmagicenhet)
09:54:39.020: adding 21 milliseconds of audio buffering, total audio buffering is now 533 milliseconds (source: Blackmagicenhet)
09:54:39.830: adding 21 milliseconds of audio buffering, total audio buffering is now 554 milliseconds (source: Blackmagicenhet)
09:54:40.230: adding 21 milliseconds of audio buffering, total audio buffering is now 576 milliseconds (source: Blackmagicenhet)
09:54:43.323: adding 21 milliseconds of audio buffering, total audio buffering is now 597 milliseconds (source: Blackmagicenhet)
11:56:20.015: adding 21 milliseconds of audio buffering, total audio buffering is now 618 milliseconds (source: Blackmagicenhet)
11:56:20.609: adding 21 milliseconds of audio buffering, total audio buffering is now 640 milliseconds (source: Blackmagicenhet)
11:56:22.045: adding 21 milliseconds of audio buffering, total audio buffering is now 661 milliseconds (source: Blackmagicenhet)
11:56:25.474: adding 21 milliseconds of audio buffering, total audio buffering is now 682 milliseconds (source: Blackmagicenhet)
11:56:26.605: adding 21 milliseconds of audio buffering, total audio buffering is now 704 milliseconds (source: Blackmagicenhet)