Could be an under-powered computer for real-time video encoding?
or you might have a mis-match of audio sampling rates across audio sources and speakers (check your logs)
And if you are trying to boot-leg copy-protected videos, you probably won't get much help on these forums (as highly frowned upon)
If you have another use case, the following the pinned post about posting your OBS record/stream logs would be a next step, along with posting some context of your setup
In general, OBS is a compositing tool to combine (composite) multiple sources, and configure real-time video and audio effects on video and audio sources. For recording something someone else is streaming, OBS isn't the right tool (it can do it, but is a sledgehammer instead of more appropriate fly-swatter, so to speak) . if watching a video with embedded audio, why would you use an external microphone? I'm not understanding your use case to provide better help
