// 编码完成回调
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;
    }
    ViewController* encoder = (__bridge ViewController*)outputCallbackRefCon;
    bool keyframe = !CFDictionaryContainsKey( (CFArrayGetValueAtIndex(CMSampleBufferGetSampleAttachmentsArray(sampleBuffer, true), 0)), kCMSampleAttachmentKey_NotSync);
    
    // 判断当前帧是否为关键帧
    // 获取sps & pps数据
    if (keyframe)
    {
        CMFormatDescriptionRef format = CMSampleBufferGetFormatDescription(sampleBuffer);
        size_t sparameterSetSize, sparameterSetCount;
        const uint8_t *sparameterSet;
        OSStatus statusCode = CMVideoFormatDescriptionGetH264ParameterSetAtIndex(format, 0, &sparameterSet, &sparameterSetSize, &sparameterSetCount, 0 );
        if (statusCode == noErr)
        {
            // 获得了sps，再获取pps
            size_t pparameterSetSize, pparameterSetCount;
            const uint8_t *pparameterSet;
            OSStatus statusCode = CMVideoFormatDescriptionGetH264ParameterSetAtIndex(format, 1, &pparameterSet, &pparameterSetSize, &pparameterSetCount, 0 );
            if (statusCode == noErr)
            {
                // 获取SPS和PPS data
                NSData *sps = [NSData dataWithBytes:sparameterSet length:sparameterSetSize];
                NSData *pps = [NSData dataWithBytes:pparameterSet length:pparameterSetSize];
                if (encoder)
                {
                    [encoder gotSpsPps:sps pps:pps];
                }
            }
        }
    }
    
    CMBlockBufferRef dataBuffer = CMSampleBufferGetDataBuffer(sampleBuffer);
    size_t length, totalLength;
    char *dataPointer;
    
    //这里获取了数据指针，和NALU的帧总长度，前四个字节里面保存的
    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;
            // 读取NALU长度的数据
            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 gotEncodedData:data];
            
            // 移动到下一个NALU单元
            bufferOffset += AVCCHeaderLength + NALUnitLength;
        }
    }
    
}

//填充SPS和PPS数据
- (void)gotSpsPps:(NSData*)sps pps:(NSData*)pps
{
    NSLog(@"gotSpsPps %d %d", (int)[sps length], (int)[pps length]);
    const char bytes[] = "\x00\x00\x00\x01";
    size_t length = (sizeof bytes) - 1; //string literals have implicit trailing ‘\0‘
    NSData *ByteHeader = [NSData dataWithBytes:bytes length:length];
  //写入startcode
    [self.h264FileHandle writeData:ByteHeader];
    [self.h264FileHandle writeData:sps];
  //写入startcode
    [self.h264FileHandle writeData:ByteHeader];
    [self.h264FileHandle writeData:pps];
    
}

//填充NALU数据
- (void)gotEncodedData:(NSData*)data
{
    NSLog(@"gotEncodedData %d", (int)[data length]);
    if (self.h264FileHandle != NULL)
    {
        const char bytes[] = "\x00\x00\x00\x01";
        size_t length = (sizeof bytes) - 1; //string literals have implicit trailing ‘\0‘
        NSData *ByteHeader = [NSData dataWithBytes:bytes length:length];
        //写入startcode
        [self.h264FileHandle writeData:ByteHeader];
        //写入NALU数据
        [self.h264FileHandle writeData:data];
    }
}

结束编码后销毁session

- (void)EndVideoToolBox
{
    VTCompressionSessionCompleteFrames(encodingSession, kCMTimeInvalid);
    VTCompressionSessionInvalidate(encodingSession);
    CFRelease(encodingSession);
    encodingSession = NULL;
}

这样就完成了使用VideoToolbox 的H264编码。编码好的H264文件可以从沙盒中取出。

总结

仅仅看流程不看代码肯定是学不会框架的，自己动手编码试试吧！
Demo下载地址：iOS-VideoToolBox-demo