save the audio file in the background

Question

I have an app that changes the pitch of the audio when the pitch button is selected, now i am using installTapOnBus to save the file but this method gets invoca

Answer 1

Actually we made mistake in the settings of Output Audio File. The output audio file processing format should be same like as the input file(which u put effect or pitch).

And the Output file format should be in the wav or caf format. This format only save to the output audio file.

 - (IBAction)save_it_after_changes:(id)sender
    {

             engine = [[AVAudioEngine alloc] init];
             audio_player_node= [[AVAudioPlayerNode alloc] init];
            [engine attachNode:audio_player_node];
            [self setupEQ];

            AVAudioMixerNode *mixerNode = [engine mainMixerNode];
            [engine connect:audio_player_node to:unitEq format:audioFile.processingFormat];
            [engine connect:unitEq to:mixerNode format:audioFile.processingFormat];

            NSError *error12;
            [engine startAndReturnError:&error12];
            if (!error12)
            {
                  NSLog(@"Engine = %@",engine);
                 [audio_player_node scheduleFile:audioFile atTime:nil completionHandler:nil];
                 NSMutableDictionary *recordSetting = [[NSMutableDictionary alloc] init];

                  [recordSetting setValue :[NSNumber numberWithInt:kAudioFormatLinearPCM] forKey:AVFormatIDKey];
                  [recordSetting setValue:[NSNumber numberWithFloat:44100.0] forKey:AVSampleRateKey];
                  [recordSetting setValue:[NSNumber numberWithInt: 2] forKey:AVNumberOfChannelsKey];

                  [recordSetting setValue :[NSNumber numberWithInt:16] forKey:AVLinearPCMBitDepthKey];
                  [recordSetting setValue :[NSNumber numberWithBool:NO] forKey:AVLinearPCMIsBigEndianKey];
                  [recordSetting setValue :[NSNumber numberWithBool:NO] forKey:AVLinearPCMIsFloatKey];


                  NSError *error;
                 outputFile = [[AVAudioFile alloc] initForWriting:[self testFilePathURL] settings:recordSetting error:&error];
                  NSLog(@"outputfile = %@",outputFile);
                  if (error)
                  {
                         NSLog(@"outputFile error = %@",error);
                  }
                  else
                  { //(AVAudioFrameCount)audioFile.length
                        [audio_player_node installTapOnBus:0 bufferSize:8192  format:audioFile.processingFormat block:^(AVAudioPCMBuffer *buffer, AVAudioTime *when) {
                              NSLog(@"Buffer Size = %@",buffer);
                              NSLog(@"when = %lld",when.sampleTime);
                              NSLog(@"outputfile length = %lli",outputFile.length);
                              NSLog(@"input file length = %lld",audioFile.length);
                              if (outputFile.length 0) ? [paths objectAtIndex:0] : nil;
      return basePath;
}

//------------------------------------------------------------------------------

- (NSURL *)testFilePathURL
{
      return [NSURL fileURLWithPath:[NSString stringWithFormat:@"%@/test.caf",
                                     [self applicationDocumentsDirectory]]];
}

Please play the file after successfully saved. It works for me. check it out.

Please refer below link, I get more from here, Can I use AVAudioEngine to read from a file, process with an audio unit and write to a file, faster than real-time?

refer this sample project. It is what we are looking for https://github.com/VladimirKravchenko/AVAudioEngineOfflineRender