x264是一种免费的、具有更优秀算法的符合H.264/MPEG-4 AVC视频压缩编码标准格式的编码库。它同xvid一样都是开源项目，但x264是采用H.264标准的，而xvid是采用MPEG-4早期标准的。由于H.264是2003年正式发布的最新的视频编码标准，因此，在通常情况下，x264压缩出的视频文件在相同质量下要比xvid压缩出的文件要小，或者也可以说，在相同体积下比xvid压缩出的文件质量要好。它符合GPL许可证。
iOS视频编码分为硬编码和软编码：硬编码就是利用手机专用的硬件进行编码，软编码是用CPU进行编码。由于苹果在iOS8开放的硬编码的API，故现在大多数的直播应用都是采用的硬编码。
iOS硬编码
从iOS8开始，苹果开放了硬解码和硬编码API，框架为 VideoToolbox.framework， 此框架需要在iOS8及以上的系统上才能使用。
此框架中的硬解码API是几个纯C函数，在任何OC或者 C++代码里都可以使用。使用的时候，首先，要把VideoToolbox.framework 添加到工程里，并且在要使用该API的文件中包含头文件#include
直接上代码来说明，首先是定义了编码所需的变量
@interface CLHardwareVideoEncoder (){
VTCompressionSessionRef compressionSession;
NSInteger frameCount;
NSData *sps;
NSData *pps;
FILE *fp;
BOOL enabledWriteVideoFile;
}
@property (nonatomic, strong) CLLiveVideoConfiguration *configuration;
@property (nonatomic,weak) id h264Delegate;
@property (nonatomic) BOOL isBackGround;
@property (nonatomic) NSInteger currentVideoBitRate;
@end
初始化编码session
- (void)initCompressionSession{
if(compressionSession){
VTCompressionSessionCompleteFrames(compressionSession, kCMTimeInvalid);
VTCompressionSessionInvalidate(compressionSession);
CFRelease(compressionSession);
compressionSession = NULL;
}
OSStatus status = VTCompressionSessionCreate(NULL, _configuration.videoSize.width, _configuration.videoSize.height, kCMVideoCodecType_H264, NULL, NULL, NULL, VideoCompressonOutputCallback, (__bridge void *)self, &compressionSession);
if(status != noErr){
return;
}
_currentVideoBitRate = _configuration.videoBitRate;
VTSessionSetProperty(compressionSession, kVTCompressionPropertyKey_MaxKeyFrameInterval,(__bridge CFTypeRef)@(_configuration.videoMaxKeyframeInterval));
VTSessionSetProperty(compressionSession, kVTCompressionPropertyKey_MaxKeyFrameIntervalDuration,(__bridge CFTypeRef)@(_configuration.videoMaxKeyframeInterval));
VTSessionSetProperty(compressionSession, kVTCompressionPropertyKey_ExpectedFrameRate, (__bridge CFTypeRef)@(_configuration.videoFrameRate));
VTSessionSetProperty(compressionSession, kVTCompressionPropertyKey_AverageBitRate, (__bridge CFTypeRef)@(_configuration.videoBitRate));
NSArray *limit = @[@(_configuration.videoBitRate * 1.5/8),@(1)];
VTSessionSetProperty(compressionSession, kVTCompressionPropertyKey_DataRateLimits, (__bridge CFArrayRef)limit);
VTSessionSetProperty(compressionSession, kVTCompressionPropertyKey_RealTime, kCFBooleanFalse);
VTSessionSetProperty(compressionSession, kVTCompressionPropertyKey_ProfileLevel, kVTProfileLevel_H264_Main_AutoLevel);
VTSessionSetProperty(compressionSession, kVTCompressionPropertyKey_AllowFrameReordering, kCFBooleanFalse);
VTSessionSetProperty(compressionSession, kVTCompressionPropertyKey_H264EntropyMode, kVTH264EntropyMode_CABAC);
VTCompressionSessionPrepareToEncodeFrames(compressionSession);
}
编码输入
- (void)encodeVideoData:(CVImageBufferRef)pixelBuffer timeStamp:(uint64_t)timeStamp{
if(_isBackGround) return;
frameCount ++;
CMTime presentationTimeStamp = CMTimeMake(frameCount, (int32_t)_configuration.videoFrameRate);
VTEncodeInfoFlags flags;
CMTime duration = CMTimeMake(1, (int32_t)_configuration.videoFrameRate);
NSDictionary *properties = nil;
if(frameCount % (int32_t)_configuration.videoMaxKeyframeInterval == 0){
properties = @{(__bridge NSString *)kVTEncodeFrameOptionKey_ForceKeyFrame: @YES};
}
NSNumber *timeNumber = @(timeStamp);
VTCompressionSessionEncodeFrame(compressionSession, pixelBuffer, presentationTimeStamp, duration, (__bridge CFDictionaryRef)properties, (__bridge_retained void *)timeNumber, &flags);
}
回调
static void VideoCompressonOutputCallback(void *VTref, void *VTFrameRef, OSStatus status, VTEncodeInfoFlags infoFlags, CMSampleBufferRef sampleBuffer)
{
if(!sampleBuffer) return;
CFArrayRef array = CMSampleBufferGetSampleAttachmentsArray(sampleBuffer, true);
if(!array) return;
CFDictionaryRef dic = (CFDictionaryRef)CFArrayGetValueAtIndex(array, 0);
if(!dic) return;
BOOL keyframe = !CFDictionaryContainsKey(dic, kCMSampleAttachmentKey_NotSync);
uint64_t timeStamp = [((__bridge_transfer NSNumber*)VTFrameRef) longLongValue];
CLHardwareVideoEncoder *videoEncoder = (__bridge CLHardwareVideoEncoder *)VTref;
if(status != noErr){
return;
}
if (keyframe && !videoEncoder->sps)
{
CMFormatDescriptionRef format = CMSampleBufferGetFormatDescription(sampleBuffer);
size_t sparameterSetSize, sparameterSetCount;
const uint8_t *sparameterSet;
OSStatus statusCode = CMVideoFormatDescriptionGetH264ParameterSetAtIndex(format, 0, &sparameterSet, &sparameterSetSize, &sparameterSetCount, 0 );
if (statusCode == noErr)
{
size_t pparameterSetSize, pparameterSetCount;
const uint8_t *pparameterSet;
OSStatus statusCode = CMVideoFormatDescriptionGetH264ParameterSetAtIndex(format, 1, &pparameterSet, &pparameterSetSize, &pparameterSetCount, 0 );
if (statusCode == noErr)
{
videoEncoder->sps = [NSData dataWithBytes:sparameterSet length:sparameterSetSize];
videoEncoder->pps = [NSData dataWithBytes:pparameterSet length:pparameterSetSize];
if(videoEncoder->enabledWriteVideoFile){
NSMutableData *data = [[NSMutableData alloc] init];
uint8_t header[] = {0x00,0x00,0x00,0x01};
[data appendBytes:header length:4];
[data appendData:videoEncoder->sps];
[data appendBytes:header length:4];
[data appendData:videoEncoder->pps];
fwrite(data.bytes, 1,data.length,videoEncoder->fp);
}
}
}
}
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) {
// Read the NAL unit length
uint32_t NALUnitLength = 0;
memcpy(&NALUnitLength, dataPointer + bufferOffset, AVCCHeaderLength);
NALUnitLength = CFSwapInt32BigToHost(NALUnitLength);
CLVideoFrame *videoFrame = [CLVideoFrame new];
videoFrame.timestamp = timeStamp;
videoFrame.data = [[NSData alloc] initWithBytes:(dataPointer + bufferOffset + AVCCHeaderLength) length:NALUnitLength];
videoFrame.isKeyFrame = keyframe;
videoFrame.sps = videoEncoder->sps;
videoFrame.pps = videoEncoder->pps;
if(videoEncoder.h264Delegate && [videoEncoder.h264Delegate respondsToSelector:@selector(videoEncoder:videoFrame:)]){
[videoEncoder.h264Delegate videoEncoder:videoEncoder videoFrame:videoFrame];
}
if(videoEncoder->enabledWriteVideoFile){
NSMutableData *data = [[NSMutableData alloc] init];
if(keyframe){
uint8_t header[] = {0x00,0x00,0x00,0x01};
[data appendBytes:header length:4];
}else{
uint8_t header[] = {0x00,0x00,0x01};
[data appendBytes:header length:3];
}
[data appendData:videoFrame.data];
fwrite(data.bytes, 1,data.length,videoEncoder->fp);
}
bufferOffset += AVCCHeaderLength + NALUnitLength;
}
}
}
iOS软编码(待续)
转载请注明原地址，Clang的博客：https://chenhu1001.github.io 谢谢！