iphone - 我可以从 MPMusicPlayerController 获取 Audio Session /应用音频单元进行播放吗？

Question

我想控制来自 MPMusicPlayerController 的音频(即从 iPod 库播放)。例如，我想对其应用 EQ 或进行 DSP、混响之类的事情。

这可能吗？有我可以掌握的 Audio Session 吗？或者，也许有某种方法可以使用 AVAudioPlayer 播放 iPod 库中的文件？

Answer 1

MPMusicPLayerController 不能与 AV 框架“很好地”工作我设法使用 MPMusicPlayerController 获取一些 DSP 来获取媒体项目，然后获取该项目的 url。然后使用 AVURLAsset和 AVAssetReader。像这样的东西:

MPMediaItem *currentSong = [myMusicController nowPlayingItem];
NSURL *currentSongURL = [currentSong valueForProperty:MPMediaItemPropertyAssetURL];
AVURLAsset *songAsset = [AVURLAsset URLAssetWithURL:currentSongURL options:nil];
NSError *error = nil;        
AVAssetReader* reader = [[AVAssetReader alloc] initWithAsset:songAsset error:&error];

AVAssetTrack* track = [[songAsset tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0];

NSMutableDictionary* audioReadSettings = [NSMutableDictionary dictionary];
[audioReadSettings setValue:[NSNumber numberWithInt:kAudioFormatLinearPCM]
                     forKey:AVFormatIDKey];

AVAssetReaderTrackOutput* readerOutput = [AVAssetReaderTrackOutput assetReaderTrackOutputWithTrack:track outputSettings:audioReadSettings];
[reader addOutput:readerOutput];
[reader startReading];
CMSampleBufferRef sample = [readerOutput copyNextSampleBuffer];
while( sample != NULL )
{
    sample = [readerOutput copyNextSampleBuffer];

    if( sample == NULL )
        continue;

    CMBlockBufferRef buffer = CMSampleBufferGetDataBuffer( sample );
    CMItemCount numSamplesInBuffer = CMSampleBufferGetNumSamples(sample);

    AudioBufferList audioBufferList;

    CMSampleBufferGetAudioBufferListWithRetainedBlockBuffer(sample,
                                                            NULL,
                                                            &audioBufferList,
                                                            sizeof(audioBufferList),
                                                            NULL,
                                                            NULL,
                                                            kCMSampleBufferFlag_AudioBufferList_Assure16ByteAlignment,
                                                            &buffer
                                                            );

    for (int bufferCount=0; bufferCount < audioBufferList.mNumberBuffers; bufferCount++) {
        SInt16* samples = (SInt16 *)audioBufferList.mBuffers[bufferCount].mData;
        for (int i=0; i < numSamplesInBuffer; i++) {
            NSLog(@"%i", samples[i]);
        }
    }

    //Release the buffer when done with the samples 
    //(retained by CMSampleBufferGetAudioBufferListWithRetainedblockBuffer)
    CFRelease(buffer);             

    CFRelease( sample );