More and more frequently, the videos I download from YouTube using RealPlayer are in .mp4 format rather than .flv.  Normally, this isn't a problem, but in the last month or so, they are unreadable on RealPlayer, Applian FLV viewer, Microsoft Media Player, Quicktime Player, and every other media program I can imagine.  Not only that, Real can't convert to a playable format, I can't open in Vegas Studio or Pazera converter to change it to a playable format, and other programs also don't work.  Does anyone know if there is a new mpeg format incompatible with the old format, or there is some encoding that must be deciphered, or if there are any programs that play mp4 files downloaded from YouTube with RealPlayer.  I've d/l files from other sites in the same manner and they are in mp4 format, and play on every player I own.

Anyone techy enough to know the answer and help, please reply to this.  D/Ling files with Real is actually the only way I am able to watch a lot of videos, including others' brickfilms.