bd_

Yes, the original video description noted those (in Japanese) - though it's apparently still a self-playing level if you let it...

These videos were originally uploaded to nicovideo, which has a different encoding procedure (for maximum quality, you can encode your video using VP6 yourself, then upload it and have them serve it unmodified). When reuploaded by someone else to youtube, the a-v sync is often lost (a lot of backend media player stuff has flaky FLV decoding, and youtube's going to insist on re-encoding it to VP1...)

If you thought that was bad, here's what happens when someone, none the wiser, tries to play one of these levels: http://etc.uguu.us/video/jidou_furi ( automatic play version: http://etc.uguu.us/video/zenjidou_kichiku_5 - original niconico douga link: http://www.nicovideo.jp/watch/sm891777 )

Many of these videos originate from niconico douga (nicovideo.jp). Over there, さだまさし (sadamasashi) is a meme - a particular part of the BGM (played at that part of the video) sounds kinda like さだまさし if you listen /just/ right, and so people flood it in the scrolling on-screen comments at the appropriate time.

You may see でっていう (detteiu) as well, referring to the sound yoshi makes when you land on him.

To be fair, a good chunk of those could just be China filtering a shared server or something similar, and google then avoiding propagating links broken by the chinese firewall.