AVFoundation audio processing using AVPlayer's MTAudioProcessingTap with remote URLs


Staff member
There is precious little documentation on <a href="http://developer.apple.com/library/...nce/AVAudioMix_Class/Reference/Reference.html" rel="noreferrer">AVAudioMix</a> and MTAudioProcessingTap, which allow processing to be applied to the audio tracks (PCM access) of media assets in AVFoundation (on iOS). This <a href="https://chritto.wordpress.com/2013/01/07/processing-avplayers-audio-with-mtaudioprocessingtap/" rel="noreferrer">article</a> and a brief mention in a WWDC 2012 session is all I have found.

I have got the setup described <a href="https://chritto.wordpress.com/2013/01/07/processing-avplayers-audio-with-mtaudioprocessingtap/" rel="noreferrer">here</a> working for local media files but it doesn't seem to work with remote files (namely HLS streaming URLs). The only indication that this is expected is the note at the end of this <a href="http://developer.apple.com/library/ios/#qa/qa1716/_index.html" rel="noreferrer">Technical Q&amp;A</a>:

AVAudioMix only supports file-based assets.

Does any one know more about this? is there really no way of accessing the audio PCM data when the asset is not file based? Can anyone find actual Apple documentation relating to MTAudioProcessingTap?