在iOS8.0以后开放了,对图片的硬编码,要引入
@import VideoToolbox;
以下是介绍使用VTCompressionSession对接收视频数据的压缩编码;
apple developer来源
以下是步骤:
1:创建 一个compression sessioin
VTCompressionSessionCreate(CFAllocatorRef _Nullable allocator,//分配器,如果使用NULL的话,就使用默认的.
int32_t width,//视频帧的象素宽
int32_t height,//视频帧的象素高
CMVideoCodecType codecType,//编码器的类型
CFDictionaryRef _Nullable encoderSpecification,//如果用指定的视频编码器,就要设置这个.使用NULL就是videoToolbox自己选择一个.
CFDictionaryRef _Nullable sourceImageBufferAttributes,//元象素缓存,如果你不要videoToolbox给你创建,就传NULL.使用非VTB分配的缓存,可以让你有机会拷贝图片数据.
CFAllocatorRef _Nullable compressedDataAllocator,//压缩数据分配器.传NULL可以使用默认的.
VTCompressionOutputCallback _Nullable outputCallback,//回调,这个方法会在另一个线程上被异步的VTCompressionSessionEncodeFrame
调用.只有在你要使VTCompressionSessionEncodeFrameWithOutputHandler去编码帧时,才可以设置为NULL.
void * _Nullable outputCallbackRefCon,//回调方法所在的实例,回调方法是全局的可以设置为NULL
VTCompressionSessionRef _Nullable * _Nonnull compressionSessionOut)//用来接收新的compression session
示例:
OSStatus status = VTCompressionSessionCreate(NULL, width, height, kCMVideoCodecType_H264, NULL, NULL, NULL, didCompressH264, (__bridge void *)(self), &EncodingSession);
if (status != 0)
{
NSLog(@"Error by VTCompressionSessionCreate ");
return ;
}
//continue...
2:(可选)配置session的属性(Compression Properties)
使用VTSessionSetProperty(_:_:_:)或VTSessionSetProperties(_:_:)
示例
VTSessionSetProperty(EncodingSession, kVTCompressionPropertyKey_RealTime, kCFBooleanTrue);//实时运行
VTSessionSetProperty(EncodingSession, kVTCompressionPropertyKey_ProfileLevel, kVTProfileLevel_H264_Baseline_4_1);
SInt32 bitRate = width*height*50; //越高效果越屌 帧数据越大
CFNumberRef ref = CFNumberCreate(kCFAllocatorDefault, kCFNumberSInt32Type, &bitRate);
VTSessionSetProperty(EncodingSession, kVTCompressionPropertyKey_AverageBitRate, ref);
CFRelease(ref);
int frameInterval = 10; //关键帧间隔 越低效果越屌 帧数据越大
CFNumberRef frameIntervalRef = CFNumberCreate(kCFAllocatorDefault, kCFNumberIntType, &frameInterval);
VTSessionSetProperty(EncodingSession, kVTCompressionPropertyKey_MaxKeyFrameInterval,frameIntervalRef);
CFRelease(frameIntervalRef);
还有其它很多,可以去属性查看
3:编码一帧
VTCompressionSessionEncodeFrame(VTCompressionSessionRef _Nonnull session,//已经被定义的compress session
CVImageBufferRef _Nonnull imageBuffer,//包含了一帧要被压缩的视频帧,这个buffer必须要有值.
CMTime presentationTimeStamp,//这一帧要显示的时间,这个会关联到采样缓存.每一个显示时间都必须要大于前一次的时间.
CMTime duration,//这一帧要显示的持续时间,会关联到采样缓存,如果你没有持续时间,传kCMTimeInvalid.
CFDictionaryRef _Nullable frameProperties,//帧属性
void * _Nullable sourceFrameRefCon,//帧的引用值,这个会被传给输出回调方法.
VTEncodeInfoFlags * _Nullable infoFlagsOut)//接受编码操作的信息,可以传NULL
示例:
- (void) encode:(CMSampleBufferRef )sampleBuffer
{
if (EncodingSession==nil||EncodingSession==NULL)
{
return;
}
dispatch_sync(aQueue, ^{
frameCount++;
CVImageBufferRef imageBuffer = (CVImageBufferRef)CMSampleBufferGetImageBuffer(sampleBuffer);
CMTime presentationTimeStamp = CMTimeMake(frameCount, 1000);
VTEncodeInfoFlags flags;
OSStatus statusCode = VTCompressionSessionEncodeFrame(EncodingSession,
imageBuffer,
presentationTimeStamp,
kCMTimeInvalid,
NULL, NULL, &flags);
if (statusCode != noErr)
{
if (EncodingSession!=nil||EncodingSession!=NULL)
{
VTCompressionSessionInvalidate(EncodingSession);
CFRelease(EncodingSession);
EncodingSession = NULL;
return;
}
}
});
}
4.强制完成一些或全部未处理的视频帧.
调用VTCompressionSessionCompleteFrames(_:_:)
VTCompressionSessionCompleteFrames(VTCompressionSessionRef _Nonnull session,//compression session
CMTime completeUntilPresentationTimeStamp) // 视频帧关联的时间
如果completeUntilPresentationTimeStamp是数字的话,包括当前时间和之前时间的帧都会在方法返回前发出(处理完)?.
如果completeUntilPresentationTimeStamp是不是数字的话,全部的未处理的帧都会在方法返回前发出(处理完?).
示例
VTCompressionSessionCompleteFrames(EncodingSession, kCMTimeInvalid);
5.当你要结果编码时.
调用VTCompressionSessionInvalidate(_:)使session无效,并用CFRelease去释放内存.
示例
VTCompressionSessionInvalidate(EncodingSession);
CFRelease(EncodingSession);
EncodingSession = NULL;
=============================================
在编码完成时会在
typedef void (*VTCompressionOutputCallback)(
void * CM_NULLABLE outputCallbackRefCon,
void * CM_NULLABLE sourceFrameRefCon,
OSStatus status,
VTEncodeInfoFlags infoFlags,
CM_NULLABLE CMSampleBufferRef sampleBuffer );
里返回,详见上面的第一条.
void didCompressH264(void *outputCallbackRefCon, void *sourceFrameRefCon, OSStatus status, VTEncodeInfoFlags infoFlags,
CMSampleBufferRef sampleBuffer )
{
if (status != 0) return;
if (!CMSampleBufferDataIsReady(sampleBuffer))
{
NSLog(@"didCompressH264 data is not ready ");
return;
}
H264HwEncoderImpl* encoder = (__bridge H264HwEncoderImpl*)outputCallbackRefCon;
CFArrayRef array = CMSampleBufferGetSampleAttachmentsArray(sampleBuffer, true);
const void * value = CFArrayGetValueAtIndex(array, 0);
bool keyframe = !CFDictionaryContainsKey(value, kCMSampleAttachmentKey_NotSync);
if (keyframe)
{
CMFormatDescriptionRef format = CMSampleBufferGetFormatDescription(sampleBuffer);
size_t sparameterSetSize, sparameterSetCount;
const uint8_t *sparameterSet;
//提取SPS<<<<<
OSStatus statusCode = CMVideoFormatDescriptionGetH264ParameterSetAtIndex(format,
0,
&sparameterSet,
&sparameterSetSize,
&sparameterSetCount,
NULL );
if (statusCode == noErr)
{
size_t pparameterSetSize, pparameterSetCount;
const uint8_t *pparameterSet;
//提取PPS<<<<<<<
OSStatus statusCode = CMVideoFormatDescriptionGetH264ParameterSetAtIndex(format, 1, &pparameterSet, &pparameterSetSize, &pparameterSetCount, 0 );
if (statusCode == noErr)
{
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];
}
}
}
}
//提取IDR<<<<<<<
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;
while (bufferOffset < totalLength - AVCCHeaderLength)
{
uint32_t NALUnitLength = 0;
memcpy(&NALUnitLength, dataPointer + bufferOffset, AVCCHeaderLength);
NALUnitLength = CFSwapInt32BigToHost(NALUnitLength);
NSData* data = [[NSData alloc] initWithBytes:(dataPointer + bufferOffset + AVCCHeaderLength) length:NALUnitLength];
[encoder->_delegate gotEncodedData:data isKeyFrame:keyframe];
bufferOffset += AVCCHeaderLength + NALUnitLength;
}
}
}
分解:
用以下方法,可以把SPS.PPS提取出来.
OSStatus statusCode = CMVideoFormatDescriptionGetH264ParameterSetAtIndex(format,
0,
&sparameterSet,
&sparameterSetSize,
&sparameterSetCount,
NULL );
用以下方法,可以把IDR提取出来,
CMBlockBufferRef dataBuffer = CMSampleBufferGetDataBuffer(sampleBuffer);
size_t length, totalLength;
char *dataPointer;//拿出来数据的格式是,头四个字节是数据长度(但字节顺序是反的),后面就是数据..可能是由多个这样的格式组成.
OSStatus statusCodeRet = CMBlockBufferGetDataPointer(dataBuffer, 0, &length, &totalLength, &dataPointer);
if (statusCodeRet == noErr) {
size_t bufferOffset = 0;
static const int AVCCHeaderLength = 4;
while (bufferOffset < totalLength - AVCCHeaderLength)
{
uint32_t NALUnitLength = 0;
memcpy(&NALUnitLength, dataPointer + bufferOffset, AVCCHeaderLength);//取出头4个字节存到NALUintLength,
NALUnitLength = CFSwapInt32BigToHost(NALUnitLength);//把字节顺序反转一下,得到数据长度.
NSData* data = [[NSData alloc] initWithBytes:(dataPointer + bufferOffset + AVCCHeaderLength) length:NALUnitLength];
[encoder->_delegate gotEncodedData:data isKeyFrame:keyframe];
bufferOffset += AVCCHeaderLength + NALUnitLength;
}
}
