最近在做的项目里有一个功能，就是拿到手机媒体库中的音频文件，并实现APP中的播放，已经转成MP3格式上传到服务器上。

首先是要能获取到ipod library中的音频。这里我用的是MPMediaQuery，在这里有一个坑，可以拿到的歌曲中有很多歌曲的AssetURL为nil，这是因为MPMediaQuery只能拿到用户通过itunes倒入进去的歌曲url。

代码如下：

// 1.创建媒体选择队列(从ipod库中读出音乐文件)

MPMediaQuery*everything = [[MPMediaQueryalloc]init];

// 2.创建读取条件(类似于对数据做一个筛选) Value：作用等同于MPMediaType枚值

MPMediaPropertyPredicate*albumNamePredicate =

[MPMediaPropertyPredicate predicateWithValue:[NSNumber numberWithInt:MPMediaTypeMusic ] forProperty: MPMediaItemPropertyMediaType];

//3.给队列添加读取条件

[everythingaddFilterPredicate:albumNamePredicate];

//4.从队列中获取符合条件的数组集合

NSArray*itemsFromGenericQuery = [everythingitems];

//5.便利解析数据

for(MPMediaItem*songinitemsFromGenericQuery) {

//歌曲名字

> NSString *songTitle = [song valueForProperty: MPMediaItemPropertyTitle];

//歌曲路径

NSString *url = [song valueForProperty: MPMediaItemPropertyAssetURL];

//歌手

NSString *songer = [song valueForProperty: MPMediaItemPropertyArtist];

}

拿到后肯定是实现APP中的播放，这个就很简单了。采用AVAudioPlayer就好了

经过一番查阅，最终找到一个办法，就是先把它转为caf 写到内存里，然后再把.caf转为.mp3 就可以上传了。这里caf转mp3需要使用第三方库：lame (lame三库的资源)

代码如下:

1.导出成caf格式，这种导出方式，文件名必须以.caf作为后缀

- (void)convertToCAF:(NSString *)songUrl name:(NSString *)songName

{

dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, 0.1 * NSEC_PER_SEC);

dispatch_after(popTime, dispatch_get_main_queue(), ^(void){

[UsingHUD showInView:self.view text:@"正在处理，请稍等..."];

});

NSURL *url = [NSURL URLWithString:songUrl];

//由于中文歌名不行 这边采用时间戳

NSString *fileName = [NSString stringWithFormat:@"%@.caf",[self getTimestamp]];

AVURLAsset *songAsset = [AVURLAsset URLAssetWithURL:url 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];

NSArray *dirs = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);

NSString *documentsDirectoryPath = [dirs objectAtIndex:0];

NSString *exportPath = [documentsDirectoryPath stringByAppendingPathComponent:fileName];

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];

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: ^

{

// 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];

//实现caf 转mp3

[self audioCAFtoMP3:exportPath];

NSLog (@"done. file size is %lld",

[outputFileAttributes fileSize]);

break;

}

}

}];

}

2.caf >mp3

- (void)audioCAFtoMP3:(NSString *)wavPath {

NSString *cafFilePath = wavPath;

NSString *mp3FilePath = [NSString stringWithFormat:@"%@.mp3",[NSString stringWithFormat:@"%@",[cafFilePath substringToIndex:cafFilePath.length - 4]]];

@try {

int read, write;

FILE *pcm = fopen([cafFilePath cStringUsingEncoding:1], "rb"); //source 被转换的音频文件位置

fseek(pcm, 4*1024, SEEK_CUR); //skip file header

FILE *mp3 = fopen([mp3FilePath cStringUsingEncoding:1], "wb"); //output 输出生成的Mp3文件位置

const int PCM_SIZE = 8192;

const int MP3_SIZE = 8192;

short int pcm_buffer[PCM_SIZE*2];

unsigned char mp3_buffer[MP3_SIZE];

lame_t lame = lame_init();

lame_set_num_channels(lame,1);//设置1为单通道，默认为2双通道

lame_set_in_samplerate(lame, 44100.0);

lame_set_VBR(lame, vbr_default);

lame_set_brate(lame,8);

lame_set_mode(lame,3);

lame_set_quality(lame,2);

lame_init_params(lame);

do {

read = fread(pcm_buffer, 2*sizeof(short int), PCM_SIZE, pcm);

if (read == 0)

write = lame_encode_flush(lame, mp3_buffer, MP3_SIZE);

else

write = lame_encode_buffer_interleaved(lame, pcm_buffer, read, mp3_buffer, MP3_SIZE);

fwrite(mp3_buffer, write, 1, mp3);

} while (read != 0);

lame_close(lame);

fclose(mp3);

fclose(pcm);

}

@catch (NSException *exception) {

NSLog(@"%@",[exception description]);

}

@finally {

dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, 0.1 * NSEC_PER_SEC);

dispatch_after(popTime, dispatch_get_main_queue(), ^(void){

[UsingHUD hideInView:self.view];

//主线程上传到oss

[self localdispose:mp3FilePath];

});

}

}

到此，大功告成～～