将 MPMEDIAITEM 转换为 OGG Vorbis

Question

我找到了（自定义我找到的方法）一种转换MpMediaItem和获取mp3文件的方法。可能这不是最好的方法，但它正在起作用。

有没有办法获取 *.ogg 文件而不是 *.mp3？正确的方法是什么？

这是我用来获取 *.mp3 文件的方法：

    -(void)exportMP3:(NSURL*)url toFileUrl:(NSString*)fileURL
{
    AVURLAsset *asset=[[AVURLAsset alloc] initWithURL:url options:nil];
    AVAssetReader *reader=[[AVAssetReader alloc] initWithAsset:asset error:nil];
    NSMutableArray *myOutputs =[[NSMutableArray alloc] init];
    for(id track in [asset tracks])
    {
        AVAssetReaderTrackOutput *output=[AVAssetReaderTrackOutput assetReaderTrackOutputWithTrack:track outputSettings:nil];
        [myOutputs addObject:output];   
        [reader addOutput:output];
    }
    [reader startReading];
    NSFileHandle *fileHandle ;
    NSFileManager *fm=[NSFileManager defaultManager];
    if(![fm fileExistsAtPath:fileURL])
    {
        [fm createFileAtPath:fileURL contents:[[NSData alloc] init] attributes:nil];
    }else{
        NSURL *url = [NSURL URLWithString:fileURL];
        [fm removeItemAtURL:url error:nil];
        [fm createFileAtPath:fileURL contents:[[NSData alloc] init] attributes:nil];
    }
    fileHandle=[NSFileHandle fileHandleForWritingAtPath:fileURL];    
    [fileHandle seekToEndOfFile];
    AVAssetReaderOutput *output=[myOutputs objectAtIndex:0];
    int totalBuff=0;
    int test = 1;
    while(test == 1)
    {
        CMSampleBufferRef ref=[output copyNextSampleBuffer];
        if(ref==NULL)
            test = 0;
        if(ref==NULL)
            break;
        //copy data to file
        //read next one
        AudioBufferList audioBufferList;
        NSMutableData *data;
        CMBlockBufferRef blockBuffer;
        CMSampleBufferGetAudioBufferListWithRetainedBlockBuffer(ref, NULL, &audioBufferList, sizeof(audioBufferList), NULL, NULL, 0, &blockBuffer);
        for( int y=0; y<audioBufferList.mNumberBuffers; y++ )
        {
            AudioBuffer audioBuffer = audioBufferList.mBuffers[y];
            void *frame = audioBuffer.mData;
            data = [[NSMutableData alloc] initWithBytes:frame length:audioBuffer.mDataByteSize];
        }
        totalBuff++;
        NSLog(@"n%dn",totalBuff);
        int time = [self.mediaPlayer durationOfCurrentItem];
        if (totalBuff * 2 <= time + 1)        
            [fileHandle writeData:data];
    }
    [fileHandle closeFile];
}

Answer 1

您可以使用 libvorbis 将 PCM 数据编码到 Vorbis。