Why is there no audio in m4v files when played in QuickTime or iTunes?

Other threads here have posed this same question, but some were closed with what seemed to me to be inconclusive or ambiguous answers. I believe I've found the reason recently and want to pass on what I learned. I used VLC to convert a miniDV video file to m4v format using the default settings. Result: a MUCH smaller file (89 MB vs 1.09GB!), but a video that played without sound in Quicktime and iTunes (it played properly in VLC). I looked at VLC's audio codec used in onversions to find it's default setting was "MPEG Audio". On a hunch I changed it to "MPEG 4 Audio (AAC)", reran the conversion and voila - video AND sound when played in Quicktime and iTunes (and VLC).

If you have no audio when playing m4v files, use video editing software like VLC to inspect the audio codec being used and change it to another codec compatible with Quicktime and iTunes.