音频格式转化 m4a 转 wav

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还是因为音频合成的原因，合成的音频是m4a 格式，上传到七牛后，形成的链接，浏览器可以播放。但是手机不行，m4a 是偏视频格式，用原有的avplayer 方法不能播放，所以需要进行转化后上传播放。

代码如下：

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-(void)convetM4aToWav:(NSURL *)originalUrl
destUrl:(NSString *)destUrlStr
completed:(void (^)(NSError *error)) completed {
NSLog(@"\n\n\nM4A-WAV\n\n\n");


if ([[NSFileManager defaultManager] fileExistsAtPath:destUrlStr]) {
[[NSFileManager defaultManager] removeItemAtPath:destUrlStr error:nil];
}
NSURL *destUrl     = [NSURL fileURLWithPath:destUrlStr];
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);
completed(error);
return;
}
AVAssetReaderOutput *assetReaderOutput = [AVAssetReaderAudioMixOutput
assetReaderAudioMixOutputWithAudioTracks:songAsset.tracks
audioSettings: nil];
if (![assetReader canAddOutput:assetReaderOutput]) {
NSLog (@"can't add reader output... die!");
completed(error);
return;
}
[assetReader addOutput:assetReaderOutput];

AVAssetWriter *assetWriter = [AVAssetWriter assetWriterWithURL:destUrl
fileType:AVFileTypeCoreAudioFormat
error:&error];
if (error) {
NSLog (@"error: %@", error);
completed(error);
return;
}
AudioChannelLayout channelLayout;
memset(&channelLayout, 0, sizeof(AudioChannelLayout));
channelLayout.mChannelLayoutTag = kAudioChannelLayoutTag_Stereo;
NSDictionary *outputSettings = [NSDictionary dictionaryWithObjectsAndKeys:
[NSNumber numberWithInt:kAudioFormatLinearPCM], AVFormatIDKey,
[NSNumber numberWithFloat:8000], AVSampleRateKey,
[NSNumber numberWithInt:2], AVNumberOfChannelsKey,
[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!");
completed(error);
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;
}
}
NSLog(@"转换结束");
// 删除临时temprecordAudio.m4a文件
NSError *removeError = nil;

if ([[NSFileManager defaultManager] fileExistsAtPath:[originalUrl path]]) {
BOOL success = [[NSFileManager defaultManager] removeItemAtPath:[originalUrl path] error:&removeError];
if (!success) {
NSLog(@"删除临时temprecordAudio.m4a文件失败:%@",removeError);
completed(removeError);
}else{
NSLog(@"删除临时temprecordAudio.m4a文件:%@成功",originalUrl);
completed(removeError);
}
}else {
NSLog(@"文件不存在");
}
}];
}

文档目录相关代码如下：

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- (NSString *)documentPath
{
NSString *documentPath = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES).lastObject;
return documentPath;
}

- (NSString *)audioCacheFolder
{
NSString *audioFolder = [[self documentPath] stringByAppendingPathComponent:AUDIOCACHE];
if (![FILEMANAGER fileExistsAtPath:audioFolder]) {
NSError *error = nil;
[FILEMANAGER createDirectoryAtPath:audioFolder withIntermediateDirectories:YES attributes:nil error:&error];
if (error) {
NSLog(@"音频文件夹创建失败----%@", error);
}
}

return audioFolder;
}
//用url作为文件名
- (NSString *)audioFilePath:(NSString *)audioURL
{
NSString *fileName = [audioURL stringByReplacingOccurrencesOfString:@"/" withString:@"-"];
return [[self audioCacheFolder] stringByAppendingPathComponent:fileName];
}