ios - Export audio file after adding an effect -

i have audio file want process using effects (like pitch effect) , write final result file.

before process file , save disc let user play pitch effect , listen changes in real time.

this how real time stuff:

    let audiosession = avaudiosession.sharedinstance()     audiosession.setcategory(avaudiosessioncategoryplayback, error: nil)     audiosession.setactive(true, error: nil)      audioengine = avaudioengine()     audiofile = avaudiofile(forreading: audiourl!, error: nil)      audioplayernode = avaudioplayernode()     audioengine.attachnode(audioplayernode)      changepitcheffect = avaudiounittimepitch()     changepitcheffect.pitch = 1.0 // default     audioengine.attachnode(changepitcheffect)      audioengine.connect(audioplayernode, to: changepitcheffect, format: nil)     audioengine.connect(changepitcheffect, to: audioengine.outputnode, format: nil)      let framecapacity = uint32(audiofile.length)     let buffer = avaudiopcmbuffer(pcmformat: audiofile.processingformat, framecapacity: framecapacity)     if audiofile.readintobuffer(buffer, error: nil) {          audioengine.startandreturnerror(nil)          audioplayernode.schedulebuffer(buffer, attime: nil, options: .loops, completionhandler: nil)          audioplayernode.play() // start playing in loop     } 

then using uislider let user change value of pitch while listening audio in loop.

so when user finish playing pitch , tap next button, need save audio file chosen pitch value.

my question is, how create new audio file pitch effect?

i don't want record while user listening audio , play pitch effect, want export final result (without playing file of course)

since using avaudiosession not explicit requirement in title of question, there 2 possible answers:

play through node (with avaudiosession)

install tap on node. see av foundation framework reference.

audioplayernode.installtaponbus(0, buffersize:framelength, format: audioinputnode.outputformatforbus(0), block: {(buffer, time) in     let channels = unsafearray(start: buffer.floatchanneldata, length: int(buffer.format.channelcount))     let floats = unsafearray(start: channels[0], length: int(buffer.framelength))      var = 0; < int(self.audiobuffer.framelength); i+=int(self.audiomixernode.outputformatforbus(0).channelcount)     {         // process     } }) 

the avaudiosession tap mechanism requires play though. more recording while playing on stack overflow answer @matt.

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use audiounit (without avaudiosession)

initialize audiosession audiosessioninitialize play & record, set read & write stream, , pass aurendercallbackstruct pointing data processing code. this, however, precludes capitalizing upon avaudiounittimepitch. can find out more solution in how realtime recording effect processing on ios article.