音频格式转化 m4a 转 wav

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：

-(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：

- (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];
}