convertToWav.m

//
//  convertToWav.m
//  MixDJ
//
//  Created by Jonathan Silverman on 2/26/19.
//  Copyright © 2019 Jonathan Silverman. All rights reserved.
//

#import <Foundation/Foundation.h>
#import <AVFoundation/AVFoundation.h>

void convertToWav(NSURL *assetURL, NSString *exportPath) {
    // set up an AVAssetReader to read from a URL
    AVURLAsset *songAsset =
    [AVURLAsset URLAssetWithURL:assetURL options:nil];
    
    NSError *assetError = nil;
    
    AVAssetReader *assetReader = [AVAssetReader assetReaderWithAsset:songAsset
                                   error:&assetError];
    if (assetError) {
        NSLog (@"error: %@", assetError);
        return;
        }
    
    AVAssetReaderOutput *assetReaderOutput =
    [AVAssetReaderAudioMixOutput
      assetReaderAudioMixOutputWithAudioTracks:songAsset.tracks
      audioSettings: nil];
    if (! [assetReader canAddOutput: assetReaderOutput]) {
        NSLog (@"can't add reader output... die!");
        return;
    }
    [assetReader addOutput: assetReaderOutput];
    if ([[NSFileManager defaultManager] fileExistsAtPath:exportPath]) {
        [[NSFileManager defaultManager] removeItemAtPath:exportPath
                                                   error:nil];
    }
    NSURL *exportURL = [NSURL fileURLWithPath:exportPath];
    
    AVAssetWriter *assetWriter =
    [AVAssetWriter assetWriterWithURL:exportURL
                              fileType:AVFileTypeWAVE
                                 error:&assetError];
    if (assetError) {
        NSLog (@"error: %@", assetError);
        return;
    }
    
    AudioChannelLayout channelLayout;
    memset(&channelLayout, 0, sizeof(AudioChannelLayout));
    channelLayout.mChannelLayoutTag = kAudioChannelLayoutTag_Stereo;
    NSDictionary *outputSettings =
    [NSDictionary dictionaryWithObjectsAndKeys:
     [NSNumber numberWithInt:kAudioFormatLinearPCM], AVFormatIDKey,
     [NSNumber numberWithFloat:44100.0], AVSampleRateKey,
     [NSNumber numberWithInt:2], AVNumberOfChannelsKey,
     [NSData dataWithBytes:&channelLayout length:sizeof(AudioChannelLayout)],
     AVChannelLayoutKey,
     [NSNumber numberWithInt:16], AVLinearPCMBitDepthKey,
     [NSNumber numberWithBool:NO], AVLinearPCMIsNonInterleaved,
     [NSNumber numberWithBool:NO],AVLinearPCMIsFloatKey,
     [NSNumber numberWithBool:NO], AVLinearPCMIsBigEndianKey,
     nil];
    
    AVAssetWriterInput *assetWriterInput =
    [AVAssetWriterInput assetWriterInputWithMediaType:AVMediaTypeAudio
                                        outputSettings:outputSettings];
    if ([assetWriter canAddInput:assetWriterInput]) {
        [assetWriter addInput:assetWriterInput];
    } else {
        NSLog (@"can't add asset writer input... die!");
        return;
    }
    assetWriterInput.expectsMediaDataInRealTime = NO;
    
    [assetWriter startWriting];
    [assetReader startReading];
    AVAssetTrack *soundTrack = [songAsset.tracks objectAtIndex:0];
    CMTime startTime = CMTimeMake (0, soundTrack.naturalTimeScale);
    [assetWriter startSessionAtSourceTime: startTime];
    
    __block UInt64 convertedByteCount = 0;
    dispatch_queue_t mediaInputQueue =
    dispatch_queue_create("mediaInputQueue", NULL);
    [assetWriterInput requestMediaDataWhenReadyOnQueue:mediaInputQueue
                                            usingBlock: ^
     {
         
         while (assetWriterInput.readyForMoreMediaData) {
             CMSampleBufferRef nextBuffer =
             [assetReaderOutput copyNextSampleBuffer];
             if (nextBuffer) {
                 // append buffer
                 [assetWriterInput appendSampleBuffer: nextBuffer];
                 // update ui
                 convertedByteCount +=
                 CMSampleBufferGetTotalSampleSize (nextBuffer);
                 NSNumber *convertedByteCountNumber =
                 [NSNumber numberWithLong:convertedByteCount];
                 NSLog(convertedByteCountNumber.stringValue);
//                 [self performSelectorOnMainThread:@selector(updateSizeLabel:)
//                                        withObject:convertedByteCountNumber
//                                     waitUntilDone:NO];
                 
             } else {
                 // done!
                 [assetWriterInput markAsFinished];
                 [assetWriter finishWriting];
                 [assetReader cancelReading];
                 NSDictionary *outputFileAttributes =
                 [[NSFileManager defaultManager]
                  attributesOfItemAtPath:exportPath
                  error:nil];
                 NSLog (@"done. file size is %ld",
                        [outputFileAttributes fileSize]);
                 NSNumber *doneFileSize = [NSNumber numberWithLong:
                                           [outputFileAttributes fileSize]];
//                 [self performSelectorOnMainThread:@selector(updateCompletedSizeLabel:)
//                                        withObject:doneFileSize
//                                     waitUntilDone:NO];
                 // release a lot of stuff
                 break;
             }
         }
     }];
    NSLog (@"bottom of convertTapped:");
}