QT to WMV problems

On a Mac, exporting qt files to wmv, the resulting wmv file is much shorter than the original, approximately 1/3 the length. What’s the fix here please?

There’s probably missing chunks in the middle of the wmv. Normally the fix on a PC would be to reindex it using asfbin, windows media encoder, or asftools. Not sure what your options would be on a Mac though.