QuickTime Player 10.x: If a movie doesn’t play properly
Some movie files, even though QuickTime Player can open them, may not play without additional software. These movie files often contain data that was created using a codec (compressor/decompressor) that QuickTime Player doesn’t support by default.
You might be able to obtain software from other manufacturers that allows QuickTime Player to play these files. For more information about obtaining software to play specific movie formats, see this Apple Support article: