VideoToolBox编码h264

创建VTCompressionSession

aQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
dispatch_sync(aQueue, ^{
//创建session
OSStatus status=
VTCompressionSessionCreate(NULL, width, height, kCMVideoCodecType_H264, NULL, NULL, NULL, didCompressH264, (__bridge
void*)(self), &EncodingSession);
if (status!=0) {
NSLog(@"创建session失败");
return ;
}
//设置session属性
//
// 设置实时编码输出（避免延迟）
VTSessionSetProperty(EncodingSession, kVTCompressionPropertyKey_RealTime, kCFBooleanTrue);
// h264 profile, 直播一般使用baseline，可减少由于b帧带来的延时
VTSessionSetProperty(EncodingSession, kVTCompressionPropertyKey_ProfileLevel, kVTProfileLevel_H264_Baseline_AutoLevel);
// 设置关键帧（GOPsize)间隔
int frameInterval = 5;
CFNumberRef
frameIntervalRef = CFNumberCreate(kCFAllocatorDefault, kCFNumberIntType, &frameInterval);
VTSessionSetProperty(EncodingSession, kVTCompressionPropertyKey_MaxKeyFrameInterval, frameIntervalRef);
// 设置帧率，只用于初始化session，不是实际FPS
int fps = 25;
CFNumberRef
fpsRef = CFNumberCreate(kCFAllocatorDefault, kCFNumberIntType, &fps);
VTSessionSetProperty(EncodingSession, kVTCompressionPropertyKey_ExpectedFrameRate, fpsRef);
//设置码率，上限，单位是bps
// 设置编码码率(比特率)，如果不设置，默认将会以很低的码率编码，导致编码出来的视频很模糊
int bitRate = width * height * 3 * 4 * 8;
CFNumberRef bitRateRef = CFNumberCreate(kCFAllocatorDefault, kCFNumberSInt32Type, &bitRate);
VTSessionSetProperty(EncodingSession, kVTCompressionPropertyKey_AverageBitRate, bitRateRef);
//设置码率，均值，单位是byte
int bitRateLimit = width * height * 3 * 4;
CFNumberRef bitRateLimitRef = CFNumberCreate(kCFAllocatorDefault, kCFNumberSInt32Type, &bitRateLimit);
VTSessionSetProperty(EncodingSession, kVTCompressionPropertyKey_DataRateLimits, bitRateLimitRef);
VTCompressionSessionPrepareToEncodeFrames(EncodingSession);
});

// 编码一帧图像，使用queue，防止阻塞系统摄像头采集线程
- (void)encode:(CMSampleBufferRef )sampleBuffer
{
dispatch_sync(aQueue, ^{
frameCount++;
// Get the CV Image buffer
CVImageBufferRef imageBuffer = (CVImageBufferRef)CMSampleBufferGetImageBuffer(sampleBuffer);
// 帧时间，如果不设置会导致时间轴过长。
CMTime presentationTimeStamp = CMTimeMake(frameCount, 1000);
//CMTime duration = CMTimeMake(1, DURATION);
// 其中 flags 用0 表示使用同步解码，这样比较简单。
VTEncodeInfoFlags flags;
// Pass it to the encoder
OSStatus statusCode = VTCompressionSessionEncodeFrame(EncodingSession,
imageBuffer,
presentationTimeStamp,
kCMTimeInvalid,
NULL, NULL, &flags);
// Check for error
if (statusCode != noErr) {
NSLog(@"H264: VTCompressionSessionEncodeFrame failed with %d", (int)statusCode);
[self End];
return;
}
//
NSLog(@"H264: VTCompressionSessionEncodeFrame Success");
});
}

void didCompressH264(void *outputCallbackRefCon, void *sourceFrameRefCon, OSStatus status, VTEncodeInfoFlags infoFlags,
CMSampleBufferRef sampleBuffer )
{
//
NSLog(@"didCompressH264 called with status %d infoFlags %d", (int)status, (int)infoFlags);
if (status != 0) return;
if (!CMSampleBufferDataIsReady(sampleBuffer))
{
NSLog(@"didCompressH264 data is not ready ");
return;
}
H264Encoder* encoder = (__bridge H264Encoder*)outputCallbackRefCon;
// 判断当前帧是否为关键帧
// 获取sps & pps数据
bool keyframe = !CFDictionaryContainsKey( (CFArrayGetValueAtIndex(CMSampleBufferGetSampleAttachmentsArray(sampleBuffer, true), 0)), kCMSampleAttachmentKey_NotSync);
if (keyframe)
{
CMFormatDescriptionRef format = CMSampleBufferGetFormatDescription(sampleBuffer);
// CFDictionaryRef extensionDict = CMFormatDescriptionGetExtensions(format);
// Get the extensions
// From the extensions get the dictionary with key "SampleDescriptionExtensionAtoms"
// From the dict, get the value for the key "avcC"
size_t sparameterSetSize, sparameterSetCount;
const uint8_t *sparameterSet;
OSStatus statusCode = CMVideoFormatDescriptionGetH264ParameterSetAtIndex(format, 0, &sparameterSet, &sparameterSetSize, &sparameterSetCount, 0 );
if (statusCode == noErr)
{
// Found sps and now check for pps
size_t pparameterSetSize, pparameterSetCount;
const uint8_t *pparameterSet;
OSStatus statusCode = CMVideoFormatDescriptionGetH264ParameterSetAtIndex(format, 1, &pparameterSet, &pparameterSetSize, &pparameterSetCount, 0 );
if (statusCode == noErr)
{
// Found pps
encoder->sps = [NSData dataWithBytes:sparameterSet length:sparameterSetSize];
encoder->pps = [NSData dataWithBytes:pparameterSet length:pparameterSetSize];
if (encoder->_delegate)
{
[encoder->_delegate gotSpsPps:encoder->sps pps:encoder->pps];
}
}
}
}
CMBlockBufferRef dataBuffer = CMSampleBufferGetDataBuffer(sampleBuffer);
size_t length, totalLength;
char *dataPointer;
OSStatus statusCodeRet = CMBlockBufferGetDataPointer(dataBuffer, 0, &length, &totalLength, &dataPointer);
if (statusCodeRet == noErr) {
size_t bufferOffset = 0;
static const int AVCCHeaderLength = 4; // 返回的nalu数据前四个字节不是0001的startcode，而是大端模式的帧长度length
// 循环获取nalu数据
while (bufferOffset < totalLength - AVCCHeaderLength) {
uint32_t NALUnitLength = 0;
// 获取nalu的长度
memcpy(&NALUnitLength, dataPointer + bufferOffset, AVCCHeaderLength);
// 从大端转系统端
NALUnitLength = CFSwapInt32BigToHost(NALUnitLength);
NSData* data = [[NSData alloc] initWithBytes:(dataPointer + bufferOffset + AVCCHeaderLength) length:NALUnitLength];
[encoder->_delegate gotEncodedData:data isKeyFrame:keyframe];
// 读取下一个nalu，一次回调可能包含多个nalu
bufferOffset += AVCCHeaderLength + NALUnitLength;
}
}
}

- (void) End
{
// Mark the completion
VTCompressionSessionCompleteFrames(EncodingSession, kCMTimeInvalid);
// End the session
VTCompressionSessionInvalidate(EncodingSession);
CFRelease(EncodingSession);
EncodingSession = NULL;
}

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