For most music videos I’ve seen, they just use the track in question with maybe some audio added here and there to tell a story in the music video - like tape identifier noise in an old album take or maybe a class scene if the video takes place at a school or something. Or maybe police sirens if you’re some bad-ass gangster tearing up the streets. But the song usually isn’t edited or modified once it gets going - maybe some foley is added during a breakdown or something, but that is going pretty far for most music videos.
I think you’re just hearing the audio compression algo in action. It seems like some might be lower quality than others, or potentially lower-quality uploads?
I admit that I didn’t listen long but I couldn’t hear much of a difference at all
Not sure what’s happening in the videos you linked to, but MP3s might be a different master (and louder initially, but less so after youtube interference) since streaming sites are pushing volume up or down based on how loud it is with specific LUFS targets or similar, so for a streaming site that pushes your audio down to -14 LUFS you can make a different master that is already at -14 LUFS (if you release DNB on something like Hospital Records the MP3 master still might go up to -5 or -4 LUFS), see this thread for more on that topic. This might also affect the Youtube processing.
I’ve seen (or heard) a lot of instances where the video comes out before the album is mastered, so the music video and single sounds way cleaner and more normal to my ears (unfortunately this should be the opposite, but it comes down to taste). I have actual references where this has happened and you’d be surprised to learn which one they kept for the entire album, like a trainwreck.
It’s easy to tell when the dynamics of the release are flat and lifeless, because the A/B comparison is like night and day. But most of the time if both are done like a normal person, I wouldn’t notice a difference unless you forced me to listen to both back to back. Honestly I don’t even think I’d notice outside of rock and metal most of the time because electronic music can kind of stand to have weird dynamics (and definitely sounds!) sometimes.