之前我使用
由于某种原因，在每次读取之间总会有一个颠簸。在我的代码中，您会注意到我每次设置时间范围时都会启动和结束AVAssetReader，这是因为在阅读器启动后我无法动态调整时间范围（有关更多详细信息，请参见此处）。
难道启动和关闭阅读器只是为了产生连续的实时体验而太昂贵了吗？还是有其他我不知道的方法可以做到这一点？
此外，请注意，无论我将时间间隔设置为什么点，都会出现这种抖动或滞后。这让我相信，以我目前的方式启动和结束读取器对于实时音频播放来说过于昂贵。
CMSampleBufferGetAudioBufferListWithRetainedBlockBuffer从完整的音频文件中读取音频样本。现在我想使用时间范围（即我指定时间范围..按照时间读取小块音频，然后返回并再次读取）来做同样的事情。我想使用时间范围的原因是我想控制每个读取的大小（以适应最大大小的数据包）。由于某种原因，在每次读取之间总会有一个颠簸。在我的代码中，您会注意到我每次设置时间范围时都会启动和结束AVAssetReader，这是因为在阅读器启动后我无法动态调整时间范围（有关更多详细信息，请参见此处）。
难道启动和关闭阅读器只是为了产生连续的实时体验而太昂贵了吗？还是有其他我不知道的方法可以做到这一点？
此外，请注意，无论我将时间间隔设置为什么点，都会出现这种抖动或滞后。这让我相信，以我目前的方式启动和结束读取器对于实时音频播放来说过于昂贵。
- (void) setupReader
{
NSURL *assetURL = [NSURL URLWithString:@"ipod-library://item/item.m4a?id=1053020204400037178"];
songAsset = [AVURLAsset URLAssetWithURL:assetURL options:nil];
track = [songAsset.tracks objectAtIndex:0];
nativeTrackASBD = [self getTrackNativeSettings:track];
// set CM time parameters
assetCMTime = songAsset.duration;
CMTimeReadDurationInSeconds = CMTimeMakeWithSeconds(1, assetCMTime.timescale);
currentCMTime = CMTimeMake(0,assetCMTime.timescale);
}
-(void)readVBRPackets
{
// make sure assetCMTime is greater than currentCMTime
while (CMTimeCompare(assetCMTime,currentCMTime) == 1 )
{
NSError * error = nil;
reader = [[AVAssetReader alloc] initWithAsset:songAsset error:&error];
readerOutput = [AVAssetReaderTrackOutput assetReaderTrackOutputWithTrack:track
outputSettings:nil];
[reader addOutput:readerOutput];
reader.timeRange = CMTimeRangeMake(currentCMTime, CMTimeReadDurationInSeconds);
[reader startReading];
while ((sample = [readerOutput copyNextSampleBuffer])) {
CMItemCount numSamples = CMSampleBufferGetNumSamples(sample);
if (numSamples == 0) {
continue;
}
NSLog(@"reading sample");
CMBlockBufferRef CMBuffer = CMSampleBufferGetDataBuffer( sample );
AudioBufferList audioBufferList;
OSStatus err = CMSampleBufferGetAudioBufferListWithRetainedBlockBuffer(
sample,
NULL,
&audioBufferList,
sizeof(audioBufferList),
NULL,
NULL,
kCMSampleBufferFlag_AudioBufferList_Assure16ByteAlignment,
&CMBuffer
);
const AudioStreamPacketDescription * inPacketDescriptions;
size_t packetDescriptionsSizeOut;
size_t inNumberPackets;
CheckError(CMSampleBufferGetAudioStreamPacketDescriptionsPtr(sample,
&inPacketDescriptions,
&packetDescriptionsSizeOut),
"could not read sample packet descriptions");
inNumberPackets = packetDescriptionsSizeOut/sizeof(AudioStreamPacketDescription);
AudioBuffer audioBuffer = audioBufferList.mBuffers[0];
for (int i = 0; i < inNumberPackets; ++i)
{
SInt64 dataOffset = inPacketDescriptions[i].mStartOffset;
UInt32 packetSize = inPacketDescriptions[i].mDataByteSize;
size_t packetSpaceRemaining;
packetSpaceRemaining = bufferByteSize - bytesFilled;
// if the space remaining in the buffer is not
// enough for the data contained in this packet
// then just write it
if (packetSpaceRemaining < packetSize)
{
[self enqueueBuffer];
}
// copy data to the audio queue buffer
AudioQueueBufferRef fillBuf = audioQueueBuffers[fillBufferIndex];
memcpy((char*)fillBuf->mAudioData + bytesFilled,
(const char*)(audioBuffer.mData + dataOffset), packetSize);
// fill out packet description
packetDescs[packetsFilled] = inPacketDescriptions[i];
packetDescs[packetsFilled].mStartOffset = bytesFilled;
bytesFilled += packetSize;
packetsFilled += 1;
// if this is the last packet, then ship it
size_t packetsDescsRemaining = kAQMaxPacketDescs - packetsFilled;
if (packetsDescsRemaining == 0) {
[self enqueueBuffer];
}
}
CFRelease(CMBuffer);
CMSampleBufferInvalidate(sample);
CFRelease(sample);
}
[reader cancelReading];
reader = NULL;
readerOutput = NULL;
currentCMTime = CMTimeAdd(currentCMTime, CMTimeReadDurationInSeconds);
}
}