I'm having big issues with random hangs up and choppy playback of m4v video files downloaded from iTunes. Most of these files are: 400-600MB. Data rate: 1.6mbits/sec. 640x360. AAC (protected) 44.1khz.
Noticed that CPU is maxed (100%) when playing back these iTunes-downloaded files.

An anomalous issue:
What's strange is that m4v downloaded from non-iTunes sources (like Miro) playback w/o issues -- including high-rez/HD files!
Also, iTunes-downloaded files, prior to about 10 months back, playback w/o issues.

The playback issue persists in either a dedicated (external) QT player (v 7.6.2) or within the latest iTunes.

Methinks Apple has recently added something to the coding of iTunes m4v files that causes these issues. Dunno what that could be, tho'.

How can I improve playback?