How to Export an audio file with effect in iOS

Question

I used AVAudioEngine to play multi audio file with effect. And I want to export this sound (include effect and multi files are playing) without recording.

How I can do that?

This is my code to use AVAudioEngine

//1. Create engine
_audioEngine  = [[AVAudioEngine alloc] init];

//2. Create player nodes , unit
_mainPlayer = [[AVAudioPlayerNode alloc] init];
_aPlayer = [[AVAudioPlayerNode alloc] init];
_bPlayer = [[AVAudioPlayerNode alloc] init];

_effectTimePitch = [[AVAudioUnitTimePitch alloc] init];
AVAudioMixerNode *mixerNode = [[AVAudioMixerNode alloc] init];

//3. Attach node to engine
[_audioEngine attachNode:_mainPlayer];
[_audioEngine attachNode:_aPlayer];
[_audioEngine attachNode:_bPlayer];
[_audioEngine attachNode:mixerNode];
[_audioEngine attachNode:_effectTimePitch];

//4. Connect player node to engine's main mixer
NSDictionary *setting = @{
                          AVFormatIDKey: @(AVAudioPCMFormatFloat32),
                          AVSampleRateKey: @(1),
                          AVNumberOfChannelsKey: @(1)
                          };
_audioFormat = [[AVAudioFormat alloc] initWithSettings:setting];

[_audioEngine connect:_mainPlayer to:mixerNode format:_audioFormat];
[_audioEngine connect:_aPlayer to:mixerNode format:_audioFormat];
[_audioEngine connect:_bPlayer to:mixerNode format:_audioFormat];
[_audioEngine connect:mixerNode to:_effectTimePitch format:_audioFormat];
[_audioEngine connect:_effectTimePitch to:_audioEngine.mainMixerNode format:_audioFormat];

//5. Start engine
NSError *error;
NSAssert([_audioEngine startAndReturnError:&error], @"couldn't start engine, %@", [error localizedDescription]);

//6 Play Audio
AVAudioFile *audioFile = [[AVAudioFile alloc] initForReading: _mainURL error: nil];
[_mainPlayer scheduleFile:audioFile atTime:nil completionHandler:nil];
AVAudioFile *aFile = [[AVAudioFile alloc] initForReading: _mainURL error: nil];
[_aPlayer scheduleFile:aFile atTime:nil completionHandler:nil];
AVAudioFile *bFile = [[AVAudioFile alloc] initForReading: _mainURL error: nil];
[_bPlayer scheduleFile:bFile atTime:nil completionHandler:nil];

[_mainPlayer play];
[_aPlayer play];
[_bPlayer play];

Answer 1

You have to set up an AVAudioFile for writing. Then you install a tap on some late point in the chain (such as your last effect node) and write from that buffer to the output file.