Harmy said:

Well, then something must have gone wrong during your conversion, because the ESB and SW MKVs are identical in terms of format.

I kind of figured. :-(

At one point I stopped the process in mid-conversion and had a partially completed m4v file for STAR WARS--roughly the first 9 minutes of the movie, and on a whim, I tested it out. It loaded into iTunes just fine--but of course, it was just the first 9 minutes. Then, when I went back in to convert the whole movie as a whole, I once again ran into the same problem I've been having all along. The m4v version, upon completion of conversion, seems to be unplayable.

I'm thinking something in the original files is somehow corrupted or damaged, but I wouldn't be able to figure out what it is, or how to fix it.