使用iPod库中的音乐录制视频

Question

我正在尝试使用AVFoundation（AVCaptureOutput + AVAssetWriter）录制视频，同时从iPod库而不是麦克风播放音频。我使用了RosyWriter示例代码并删除了AudioInput，而是设置AVAssetReader以便以非压缩格式读取歌曲，

NSDictionary *outputSettings = [NSDictionary dictionaryWithObjectsAndKeys:
                                    [NSNumber numberWithInt:kAudioFormatLinearPCM], AVFormatIDKey,
                                    [NSNumber numberWithFloat:44100.0], AVSampleRateKey,
                                    [NSNumber numberWithInt:16], AVLinearPCMBitDepthKey,
                                    [NSNumber numberWithBool:NO], AVLinearPCMIsNonInterleaved,
                                    [NSNumber numberWithBool:NO], AVLinearPCMIsFloatKey,
                                    [NSNumber numberWithBool:NO], AVLinearPCMIsBigEndianKey,
                                    nil];



    mAssetReader = [[AVAssetReader alloc] initWithAsset:mAsset error:nil];
    mAssetReaderOutput = [[AVAssetReaderTrackOutput alloc] initWithTrack:audioTrack outputSettings:outputSettings];

    if ([mAssetReader canAddOutput:mAssetReaderOutput]) {
        [mAssetReader addOutput:mAssetReaderOutput];
    } 

    [mAssetReader startReading];

然后定期轮询音频样本。但它无法正常工作。有关VideoStar或Blux Movie等应用程序如何实现的建议？