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我想從LPCM原始文件中提取通道音頻，即提取立體聲LPCM文件的左聲道和右聲道。 LPCM是16位深度，交錯式，2個通道，litle endian。從我收集的字節順序是{LeftChannel，RightChannel，LeftChannel，RightChannel ...}並且由於它是16位深度，每個通道會有2個字節的採樣對嗎？從線性PCM提取音頻通道
所以我的問題是，如果我想提取左通道，那麼我會採取在0,2,4,6 ... n * 2地址的字節？而右聲道將是1,3,4，...（n * 2 + 1）。
也提取音頻通道後，我應該提取通道的格式爲16位深度，1通道？
在此先感謝
這是被提取，所以我可能由格式造成的，我目前使用從AssetReader提取PCM音頻..此代碼工作正常與不寫它的渠道的音樂文件的代碼或東西...
NSURL *assetURL = [song valueForProperty:MPMediaItemPropertyAssetURL];
AVURLAsset *songAsset = [AVURLAsset URLAssetWithURL:assetURL options:nil];
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];
NSError *assetError = nil;
AVAssetReader *assetReader = [[AVAssetReader assetReaderWithAsset:songAsset
error:&assetError]
retain];
if (assetError) {
NSLog (@"error: %@", assetError);
return;
}
AVAssetReaderOutput *assetReaderOutput = [[AVAssetReaderAudioMixOutput
assetReaderAudioMixOutputWithAudioTracks:songAsset.tracks
audioSettings: outputSettings]
retain];
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];
//CODE TO SPLIT STEREO
[self setupAudioWithFormatMono:kAudioFormatLinearPCM];
NSString *splitExportPath = [[documentsDirectoryPath stringByAppendingPathComponent:@"monoleft.caf"] retain];
if ([[NSFileManager defaultManager] fileExistsAtPath:splitExportPath]) {
[[NSFileManager defaultManager] removeItemAtPath:splitExportPath error:nil];
}
AudioFileID mRecordFile;
NSURL *splitExportURL = [NSURL fileURLWithPath:splitExportPath];
OSStatus status = AudioFileCreateWithURL(splitExportURL, kAudioFileCAFType, &_streamFormat, kAudioFileFlags_EraseFile,
&mRecordFile);
NSLog(@"status os %d",status);
[assetReader startReading];
CMSampleBufferRef sampBuffer = [assetReaderOutput copyNextSampleBuffer];
UInt32 countsamp= CMSampleBufferGetNumSamples(sampBuffer);
NSLog(@"number of samples %d",countsamp);
SInt64 countByteBuf = 0;
SInt64 countPacketBuf = 0;
UInt32 numBytesIO = 0;
UInt32 numPacketsIO = 0;
NSMutableData * bufferMono = [NSMutableData new];
while (sampBuffer) {
AudioBufferList audioBufferList;
CMBlockBufferRef blockBuffer;
CMSampleBufferGetAudioBufferListWithRetainedBlockBuffer(sampBuffer, NULL, &audioBufferList, sizeof(audioBufferList), NULL, NULL, 0, &blockBuffer);
for (int y=0; y<audioBufferList.mNumberBuffers; y++) {
AudioBuffer audioBuffer = audioBufferList.mBuffers[y];
//frames = audioBuffer.mData;
NSLog(@"the number of channel for buffer number %d is %d",y,audioBuffer.mNumberChannels);
NSLog(@"The buffer size is %d",audioBuffer.mDataByteSize);
//Append mono left to buffer data
for (int i=0; i<audioBuffer.mDataByteSize; i= i+4) {
[bufferMono appendBytes:(audioBuffer.mData+i) length:2];
}
//the number of bytes in the mutable data containing mono audio file
numBytesIO = [bufferMono length];
numPacketsIO = numBytesIO/2;
NSLog(@"numpacketsIO %d",numPacketsIO);
status = AudioFileWritePackets(mRecordFile, NO, numBytesIO, &_packetFormat, countPacketBuf, &numPacketsIO, audioBuffer.mData);
NSLog(@"status for writebyte %d, packets written %d",status,numPacketsIO);
if(numPacketsIO != (numBytesIO/2)){
NSLog(@"Something wrong");
assert(0);
}
countPacketBuf = countPacketBuf + numPacketsIO;
[bufferMono setLength:0];
}
sampBuffer = [assetReaderOutput copyNextSampleBuffer];
countsamp= CMSampleBufferGetNumSamples(sampBuffer);
NSLog(@"number of samples %d",countsamp);
}
AudioFileClose(mRecordFile);
[assetReader cancelReading];
[self performSelectorOnMainThread:@selector(updateCompletedSizeLabel:)
withObject:0
waitUntilDone:NO];
與audiofileservices輸出格式如下：
_streamFormat.mFormatFlags = kLinearPCMFormatFlagIsSignedInteger | kLinearPCMFormatFlagIsPacked;
_streamFormat.mBitsPerChannel = 16;
_streamFormat.mChannelsPerFrame = 1;
_streamFormat.mBytesPerPacket = 2;
_streamFormat.mBytesPerFrame = 2;// (_streamFormat.mBitsPerChannel/8) * _streamFormat.mChannelsPerFrame;
_streamFormat.mFramesPerPacket = 1;
_streamFormat.mSampleRate = 44100.0;
_packetFormat.mStartOffset = 0;
_packetFormat.mVariableFramesInPacket = 0;
_packetFormat.mDataByteSize = 2;
好吧我其實已經嘗試過這一點，結果是不正確的......我用你說的提取算法，但輸出聲音失真...扭曲，因爲它聽起來「慢」... – Samuel 2011-01-09 14:19:45