最近做的app需要从iOS系统的音乐库里面拷贝选中的歌曲到APP的Documents目录下，在网上找了好久之后，终于找到两种方法，分别是可以导出成指定的格式和导出成Core Audio支持的caf格式，代码分别记录在下面。
1，导出成caf格式，这种导出方式，文件名必须以.caf作为后缀，使用其他后缀会导出失败
- (void) convertToCAF:(NSString *)filename (MPMediaItem *)song
{
NSURL *assetURL = [song valueForProperty:MPMediaItemPropertyAssetURL];
AVURLAsset *songAsset = [AVURLAsset URLAssetWithURL:assetURL options:nil];
NSError *assetError = nil;
AVAssetReader *assetReader = [[AVAssetReader assetReaderWithAsset:songAsset
error:&assetError]
retain];
if (assetError) {
NSLog (@"error: %@", assetError);
return;
}
AVAssetReaderOutput *assetReaderOutput = [[AVAssetReaderAudioMixOutput
assetReaderAudioMixOutputWithAudioTracks:songAsset.tracks
audioSettings: nil]
retain];
if (! [assetReader canAddOutput: assetReaderOutput]) {
NSLog (@"can't add reader output... die!");
return;
}
[assetReader addOutput: assetReaderOutput];
NSArray *dirs = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectoryPath = [dirs objectAtIndex:0];
NSString *exportPath = [[documentsDirectoryPath stringByAppendingPathComponent:filename] retain];
if ([[NSFileManager defaultManager] fileExistsAtPath:exportPath]) {
[[NSFileManager defaultManager] removeItemAtPath:exportPath error:nil];
}
NSURL *exportURL = [NSURL fileURLWithPath:exportPath];
AVAssetWriter *assetWriter = [[AVAssetWriter assetWriterWithURL:exportURL
fileType:AVFileTypeCoreAudioFormat
error:&assetError]
retain];
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]
retain];
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: ^
{
// NSLog (@"top of block");
while (assetWriterInput.readyForMoreMediaData) {
CMSampleBufferRef nextBuffer = [assetReaderOutput copyNextSampleBuffer];
if (nextBuffer) {
// append buffer
[assetWriterInput appendSampleBuffer: nextBuffer];
// NSLog (@"appended a buffer (%d bytes)",
// CMSampleBufferGetTotalSampleSize (nextBuffer));
convertedByteCount += CMSampleBufferGetTotalSampleSize (nextBuffer);
} else {
// done!
[assetWriterInput markAsFinished];
[assetWriter finishWriting];
[assetReader cancelReading];
NSDictionary *outputFileAttributes = [[NSFileManager defaultManager]
attributesOfItemAtPath:exportPath
error:nil];
NSLog (@"done. file size is %lld",
[outputFileAttributes fileSize]);
// release a lot of stuff
[assetReader release];
[assetReaderOutput release];
[assetWriter release];
[assetWriterInput release];
[exportPath release];
break;
}
}
}];
}
2，导出成mp3或者其他格式
- (void) convertToMp3: (MPMediaItem *)song
{
NSURL *url = [song valueForProperty:MPMediaItemPropertyAssetURL];
AVURLAsset *songAsset = [AVURLAsset URLAssetWithURL:url options:nil];
NSFileManager *fileManager = [NSFileManager defaultManager];
NSArray *dirs = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectoryPath = [dirs objectAtIndex:0];
NSLog (@"compatible presets for songAsset: %@",[AVAssetExportSession exportPresetsCompatibleWithAsset:songAsset]);
NSArray *ar = [AVAssetExportSession exportPresetsCompatibleWithAsset: songAsset];
NSLog(@"%@", ar);
AVAssetExportSession *exporter = [[AVAssetExportSession alloc]
initWithAsset: songAsset
presetName: AVAssetExportPresetAppleM4A];
NSLog (@"created exporter. supportedFileTypes: %@", exporter.supportedFileTypes);
exporter.outputFileType = @"com.apple.m4a-audio";
NSString *exportFile = [documentsDirectoryPath stringByAppendingPathComponent:[NSString stringWithFormat:@"%@.m4a",[song valueForProperty:MPMediaItemPropertyTitle]]];
NSError *error1;
if([fileManager fileExistsAtPath:exportFile])
{
[fileManager removeItemAtPath:exportFile error:&error1];
}
NSURL* exportURL = [[NSURL fileURLWithPath:exportFile] retain];
exporter.outputURL = exportURL;
// do the export
[exporter exportAsynchronouslyWithCompletionHandler:^
{
NSData *data1 = [NSData dataWithContentsOfFile:exportFile];
//NSLog(@"==================data1:%@",data1);
int exportStatus = exporter.status;
switch (exportStatus) {
case AVAssetExportSessionStatusFailed: {
// log error to text view
NSError *exportError = exporter.error;
NSLog (@"AVAssetExportSessionStatusFailed: %@", exportError);
break;
}
case AVAssetExportSessionStatusCompleted: {
NSLog (@"AVAssetExportSessionStatusCompleted");
break;
}
case AVAssetExportSessionStatusUnknown: {
NSLog (@"AVAssetExportSessionStatusUnknown");
break;
}
case AVAssetExportSessionStatusExporting: {
NSLog (@"AVAssetExportSessionStatusExporting");
break;
}
case AVAssetExportSessionStatusCancelled: {
NSLog (@"AVAssetExportSessionStatusCancelled");
break;
}
case AVAssetExportSessionStatusWaiting: {
NSLog (@"AVAssetExportSessionStatusWaiting");
break;
}
default:
{ NSLog (@"didn't get export status");
break;
}
}
}];
}
以上的代码参考了 (http://stackoverflow.com/questions/4746349/copy-ipod-music-library-audio-file-to-iphone-app-folder)[http://stackoverflow.com/questions/4746349/copy-ipod-music-library-audio-file-to-iphone-app-folder] 这个帖子， 他原帖中创建AVAssetExportSession时用的是这样的创建方式。
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