iOS-音频转换

iOS处理音频过程中有时候需要不同格式的音频进行转换，最近需要将m4a格式的音频转换成wav，在网上搜索之后代码整理如下:
<pre><code>`

• (void)convetM4aToWav:(NSURL *)originalUrl destUrl:(NSURL *)destUrl {

  AVURLAsset *songAsset = [AVURLAsset URLAssetWithURL:originalUrl options:nil];

  //读取原始文件信息
  NSError *error = nil;
  AVAssetReader *assetReader = [AVAssetReader assetReaderWithAsset:songAsset error:&error];
  if (error) {
  NSLog (@"error: %@", error);
  return;
  }

  AVAssetReaderOutput *assetReaderOutput = [AVAssetReaderAudioMixOutput
  assetReaderAudioMixOutputWithAudioTracks:songAsset.tracks
  audioSettings: nil];
  if (![assetReader canAddOutput:assetReaderOutput]) {
  NSLog (@"can't add reader output... die!");
  return;
  }
  [assetReader addOutput:assetReaderOutput];

AVAssetWriter *assetWriter = [AVAssetWriter assetWriterWithURL:destUrl
                                                       fileType:AVFileTypeCoreAudioFormat
                                                          error:&error];
if (error) {
    NSLog (@"error: %@", error);
    return;
}
AudioChannelLayout channelLayout;
memset(&channelLayout, 0, sizeof(AudioChannelLayout));
channelLayout.mChannelLayoutTag = kAudioChannelLayoutTag_Stereo;
NSDictionary *outputSettings = [NSDictionary dictionaryWithObjectsAndKeys:
                                [NSNumber numberWithInt:kAudioFormatLinearPCM], AVFormatIDKey,
                                [NSNumber numberWithFloat:16000.0], 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];
             NSLog (@"appended a buffer (%zu bytes)",
                                 CMSampleBufferGetTotalSampleSize (nextBuffer));
             convertedByteCount += CMSampleBufferGetTotalSampleSize (nextBuffer);
             
             
         } else {
             [assetWriterInput markAsFinished];
             [assetWriter finishWritingWithCompletionHandler:^{
                 
             }];
             [assetReader cancelReading];
             NSDictionary *outputFileAttributes = [[NSFileManager defaultManager]
                                                   attributesOfItemAtPath:[destUrl path]
                                                   error:nil];
             NSLog (@"FlyElephant %lld",[outputFileAttributes fileSize]);
             break;
         }
     }
     
 }];

}`</code></pre>

参考链接