在设备上导出时AVAssetExportSession缺少音轨

Question

I run the export on the simulator and everything works great. I run it on the device and the video gets exported but there's no audio. This leads me to believe that I must be using an audio format that the device doesn't support but OS X does, as the simulator uses what OS X uses. I've tried m4a, aiff, and aifc and have had no luck! Any ideas??

Answer 1

I have a very similar problem. It does not seem to do with codecs, as I made a separate test case that runs fine with the same video. There's a related question that says the problem might be in playing the same assets using MPMoviePlayerController . That got me on the right track (sort of).

In my case the trouble stem from using the assets in an AVPlayer during the export. I was not able to find the exact combination that causes the export to drop the audio track – in the separate test project the export runs fine even though the asset plays in AVPlayer at the same time. After several hours of trying to find the exact cause I gave up and simply popped the asset out of the player using replaceCurrentItemWithPlayerItem:nil during export. It's a hack, but it works.

AVFoundation is a very powerful framework, but God I wish it wasn't so finicky or at least logged more errors instead of silently producing garbage.