No audio in Quicktime Player 10.4

I can't get sound out of Quicktime Player 10.4, playing a video recorded on iPhone. I DO have audio on Quicktime movies recorded from other sources. Video was shot on iPhone 5s, and the audio format is listed as AAC, 44100hz, mono. The same video plays normally, with sound, in Quicktime Player 7.

I'm a video professional and have a lot of multimedia apps installed. Wondering if something is somehow causing this problem? I mostly use Apple software, including DVD Studio Pro from the olden days.