Attempting to play an AVI file with 4channel AC3 sound causes QT player to become nonresponsive (spinning wheel) and it must be killed with Activity Monitor.
I did this with the latest a52codec source 1.7.5 (and it also happens with the released 1.7.2)
I am not completely sure whether this is an a52codec problem, or a Perian problem, but I have a similar video with the same video characteristics but only 2-channel AC3 audio, and it works fine.
THe problem video plays fine in VLC.
I have attached a Activity Monitor sample capture taken during the spinning wheel, and pictures of the file parameters displayed by Visualhub.
I extracted 15 second portions of the problem file and a "good" file using Visualhub with pass-through settings. Unfortunately, although the audio cuts out a couple of seconds into the segment of the bad file, it doesn't cause the freezing behaviour I see with the full file.
The video files are episodes of Lost. The "bad" file is episode 18, the "good" file is episode 17. Both seem to have been encoded by the same person, though the "bad" file has the 4-channel audio.