Question

我知道现在可以从用户的音乐库中取一首歌并通过改变速度，音高等进行编辑，但我似乎找不到链接到有关如何访问歌曲原始数据的有用教程。有人可以指导我这样的事情，或者是否有这样的图书馆？谢谢！

Answer 1

以下是一些您可以开始使用的源代码：

- (void) doSomethingWithAssett:(AVURLAsset *)songAsset {

NSError * error = nil;


AVAssetReader * reader = [[AVAssetReader alloc] initWithAsset:songAsset error:&error];

if (error) {
    NSLog(@"%@", [error description]);
}

AVAssetTrack * songTrack = [songAsset.tracks objectAtIndex:0];

NSDictionary* outputSettingsDict = [[NSDictionary alloc] initWithObjectsAndKeys:

                                    [NSNumber numberWithInt:kAudioFormatLinearPCM],AVFormatIDKey,
                                    //     [NSNumber numberWithInt:44100.0],AVSampleRateKey, /*Not Supported*/
                                    //     [NSNumber numberWithInt: 2],AVNumberOfChannelsKey,    /*Not Supported*/

                                    [NSNumber numberWithInt:16],AVLinearPCMBitDepthKey,
                                    [NSNumber numberWithBool:NO],AVLinearPCMIsBigEndianKey,
                                    [NSNumber numberWithBool:NO],AVLinearPCMIsFloatKey,
                                    [NSNumber numberWithBool:NO],AVLinearPCMIsNonInterleaved,

                                    nil];


AVAssetReaderTrackOutput* output = [[AVAssetReaderTrackOutput alloc] initWithTrack:songTrack outputSettings:outputSettingsDict];

[reader addOutput:output];

UInt32 sampleRate,channelCount;

NSArray* formatDesc = songTrack.formatDescriptions;
for(unsigned int i = 0; i < [formatDesc count]; ++i) {
    CMAudioFormatDescriptionRef item = (__bridge CMAudioFormatDescriptionRef)[formatDesc objectAtIndex:i];
    const AudioStreamBasicDescription* fmtDesc = CMAudioFormatDescriptionGetStreamBasicDescription (item);
    if(fmtDesc ) {

        sampleRate = fmtDesc->mSampleRate;
        channelCount = fmtDesc->mChannelsPerFrame;

        //    NSLog(@"channels:%u, bytes/packet: %u, sampleRate %f",fmtDesc->mChannelsPerFrame, fmtDesc->mBytesPerPacket,fmtDesc->mSampleRate);
    }
}


UInt32 bytesPerSample = 2 * channelCount;
SInt16 normalizeMax = 0;

NSMutableData * fullSongData = [[NSMutableData alloc] init];
[reader startReading];


UInt64 totalBytes = 0; 


SInt64 totalLeft = 0;
SInt64 totalRight = 0;
NSInteger sampleTally = 0;

NSInteger samplesPerPixel = sampleRate / 50;


while (reader.status == AVAssetReaderStatusReading){

    AVAssetReaderTrackOutput * trackOutput = (AVAssetReaderTrackOutput *)[reader.outputs objectAtIndex:0];
    CMSampleBufferRef sampleBufferRef = [trackOutput copyNextSampleBuffer];

    if (sampleBufferRef){
        CMBlockBufferRef blockBufferRef = CMSampleBufferGetDataBuffer(sampleBufferRef);

        size_t length = CMBlockBufferGetDataLength(blockBufferRef);
        totalBytes += length;


        @autoreleasepool {
            NSMutableData * data = [NSMutableData dataWithLength:length];
            CMBlockBufferCopyDataBytes(blockBufferRef, 0, length, data.mutableBytes);


            SInt16 * samples = (SInt16 *) data.mutableBytes;

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iOS - 访问可修改的原始音乐库数据？

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