AVPlayer audio stops after bitrate spike

Question

My iOS app uses AVPlayer to decode H.264 videos with AAC audio tracks out of local device storage. Content with bit rate spikes cause audio to drop shortly (less than a second) after the spike is played, yet video playback continues normally. Playing the videos through Safari seems to work fine, and this behavior is repeatable on several models of iPhones ranging from 6s through 8 plus.

I've been looking for any messages generated, delegates called with error information, or interesting KVOs, but there's been no helpful information so far. What might I do to get some sort of more detailed information that can point me in the right direction?

Answer 1

Turned out that the AVPlayer was configured to utilize methods for loading data in a custom way. The implementation of these methods failed to follow the pattern of satisfying the requests completely. (Apple docs are a vague about this.) The video portion of the AVPlayer asked for more data repeatedly, so eventually all its data got pulled. However, the audio portion patiently waited for the data to come in because there were neither an error state reported nor was all the data provided -- the presumption being that it was pending.

So, in short, sounds like there's provisions in the video handling code to treat missing data as a stall of some form and to plow onward, whereas audio doesn't have that feature. Not a bad design -- if audio cuts out it's very noticeable, and it's also by far the smaller stream so it's much less likely.

Despite spending quite a few days on the problem before posting, the lack of any useful signals made it hard to chase down the problem. I eventually reasoned that if there's no error in producing output from the stream, the problem must be in the delivery of the stream, and the problem revealed itself once I started tweaking the data loading code.