2 byte shorter userdata for mpeg4
in the past it was startcode,string,00,7F,startcode
now it is startcode,string,stratcode
both are mpeg4 compliant, as according to the standard the userdata lasts until the next 00 00 01 (startcode prefix) but some very primitive decoders which simply skip until the first 00 byte and then expect the next valid startcode might fail with the old variant, just a theory though (didnt test if quicktime can decode it now)

Originally committed as revision 2767 to svn://svn.ffmpeg.org/ffmpeg/trunk
