I've just saved a speedrunning video,and it's sound was not very clear(probably because I didn't use OBS).Would it be rejected?

It might get rejected but I am not should just don't get your hopes up

It depends on how low quality it is. Generally I would say it would be accepted. To put this into perspective, many legal runs have been submitted that are literally a cellphone camera pointed at a tv.

What about late sounds I have that problem

Submit it and see what happens! Usually as long as sound is present it's OK