Couple things, I wonder if they are tied together.
When I play something from my library on PS4, it defaults to 720 at 4mbps. I click over to the settings on the PS4 and change it to Original Quality for playback, but while the video fixes itself after that, the sound completely goes out.
I have no such issue of either on other players. When I play it on my FireTV, the same file, defaults to Original Quality and even after I change quality, the sound never disappears.