iOS 儲存攝像頭H264視訊流

weixin_33806914發表於2018-11-21
iOS

我們下面完成獲取攝像頭資料，並儲存為h264格式的檔案。

1、初始化獲取攝像頭資料相關程式碼

{
    //建立AVCaptureDevice的視訊裝置物件
    AVCaptureDevice* videoDevice = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
    
    NSError* error;
    //建立視訊輸入端物件
    AVCaptureDeviceInput* input = [AVCaptureDeviceInput deviceInputWithDevice:videoDevice error:&error];
    if (error) {
        NSLog(@"建立輸入端失敗,%@",error);
        return;
    }
    
    //建立功能會話物件
    self.captureSession = [[AVCaptureSession alloc] init];
    //設定會話輸出的視訊解析度
    [self.captureSession setSessionPreset:AVCaptureSessionPreset1280x720];
    
    //新增輸入端
    if (![self.captureSession canAddInput:input]) {
        NSLog(@"輸入端新增失敗");
        return;
    }
    [self.captureSession addInput:input];
    
    //顯示攝像頭捕捉到的資料
    AVCaptureVideoPreviewLayer* layer = [[AVCaptureVideoPreviewLayer alloc] initWithSession:self.captureSession];
    layer.frame = CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height - 100);
    [self.view.layer addSublayer:layer];
    
    //建立輸出端
    AVCaptureVideoDataOutput *videoDataOutput = [[AVCaptureVideoDataOutput alloc] init];
    //會話物件新增輸出端
    if ([self.captureSession canAddOutput:videoDataOutput]) {
        [self.captureSession addOutput:videoDataOutput];
        self.videoDataOutput = videoDataOutput;
        //建立輸出呼叫的佇列
        dispatch_queue_t videoDataOutputQueue = dispatch_queue_create("videoDataOutputQueue", DISPATCH_QUEUE_SERIAL);
        self.videoDataOutputQueue = videoDataOutputQueue;
        //設定代理和呼叫的佇列
        [self.videoDataOutput setSampleBufferDelegate:self queue:videoDataOutputQueue];
        //設定延時丟幀
        self.videoDataOutput.alwaysDiscardsLateVideoFrames = NO;
    }
}

然後我們實行代理方法

- (void)captureOutput:(AVCaptureOutput *)output didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection;

在代理方法裡面可以獲取到我們需要的CMSampleBufferRef物件。
我們呼叫會話的開始方法就可以獲取到視訊資料了。

[self.captureSession startRunning];

獲取到CMSampleBufferRef物件後，我們對CMSampleBufferRef物件進行處理。

2、建立硬解碼VideoToolBox會話物件

根據蘋果文件，我們可以知道攝像頭返回的資料為CVPixelBuffers資料，需要我們進行手動壓縮為H264資料。


3222019-3600a9d5466b92f1.png
圖片.png

在此，我們使用VideoToolBox對資料進行壓縮，我們也可以使用x264庫對資料進行壓縮。使用VideoToolBox可以進行硬編碼，效能更優，使用x264則相容性更高。
VideoToolBox為一套C語言函式庫，使用相對有點複雜。流程如下：

{
    
    self.frameID = 0;
    
    int width = (int)self.width;
    int height = (int)self.height;
    //建立編碼會話物件
    //第八個引數為回撥函式的函式名
    OSStatus status = VTCompressionSessionCreate(NULL,
                                                 width,
                                                 height,
                                                 kCMVideoCodecType_H264,
                                                 NULL,
                                                 NULL,
                                                 NULL,
                                                 didCompressH264,
                                                 (__bridge void *)(self),
                                                 &self->_EncodingSession
                                                 );
 
    NSLog(@"H264: VTCompressionSessionCreate %d", (int)status);
    if (status != 0) {
        NSLog(@"H264: Unable to create a H264 session");
        self.EncodingSession = NULL;
        return ;
    }
    // 設定實時編碼輸出（避免延遲）
    VTSessionSetProperty(self->_EncodingSession, kVTCompressionPropertyKey_RealTime, kCFBooleanTrue);
    // h264 profile, 直播一般使用baseline，可減少由於b幀帶來的延時
    VTSessionSetProperty(self->_EncodingSession, kVTCompressionPropertyKey_ProfileLevel, kVTProfileLevel_H264_Baseline_AutoLevel);
    
    // 設定關鍵幀（GOPsize)間隔
    int frameInterval = (int)(self.frameRate / 2);
    CFNumberRef  frameIntervalRef = CFNumberCreate(kCFAllocatorDefault, kCFNumberIntType, &frameInterval);
    VTSessionSetProperty(self->_EncodingSession, kVTCompressionPropertyKey_MaxKeyFrameInterval, frameIntervalRef);
    
    // 設定期望幀率
    int fps = (int)self.frameRate;
    CFNumberRef fpsRef = CFNumberCreate(kCFAllocatorDefault, kCFNumberIntType, &fps);
    VTSessionSetProperty(self->_EncodingSession, kVTCompressionPropertyKey_ExpectedFrameRate, fpsRef);
    
    //不產生B幀
    VTSessionSetProperty(self->_EncodingSession, kVTCompressionPropertyKey_AllowFrameReordering, kCFBooleanFalse);
    
    // 設定編碼位元速率(位元率)，如果不設定，預設將會以很低的位元速率編碼，導致編碼出來的視訊很模糊
    // 設定位元速率，上限，單位是bps
    int bitRate = width * height * 3 * 4 * 8;
    CFNumberRef bitRateRef = CFNumberCreate(kCFAllocatorDefault, kCFNumberSInt32Type, &bitRate);
    VTSessionSetProperty(self->_EncodingSession, kVTCompressionPropertyKey_AverageBitRate, bitRateRef);
    // 設定位元速率，均值，單位是byte
    int bitRateLimit = width * height * 3 * 4;
    CFNumberRef bitRateLimitRef = CFNumberCreate(kCFAllocatorDefault, kCFNumberSInt32Type, &bitRateLimit);
    VTSessionSetProperty(self->_EncodingSession, kVTCompressionPropertyKey_DataRateLimits, bitRateLimitRef);
    
    // Tell the encoder to start encoding
    status = VTCompressionSessionPrepareToEncodeFrames(self->_EncodingSession);
    if (status == 0) {
        self.initComplete = YES;
    }else {
        NSLog(@"init compression session prepare to encode frames failure");
    } 
}

3、實現回撥函式

我們在第二步中註冊了編碼回撥的函式名，我們實行回撥函式：

void didCompressH264(void *outputCallbackRefCon, void *sourceFrameRefCon, OSStatus status, VTEncodeInfoFlags infoFlags, CMSampleBufferRef sampleBuffer) {
//在此方法中處理獲取H264編碼後的資料
}

4、編碼資料

把獲取的sampleBuffer進行編碼

- (void)encode:(CMSampleBufferRef)sampleBuffer {
    CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer);
    // 幀時間，如果不設定會導致時間軸過長。
    CMTime presentationTimeStamp = CMTimeMake(self.frameID++, 1000);
    VTEncodeInfoFlags flags;
    OSStatus statusCode = VTCompressionSessionEncodeFrame(_EncodingSession,
                                                          imageBuffer,
                                                          presentationTimeStamp,
                                                          kCMTimeInvalid,
                                                          NULL, NULL, &flags);
    if (statusCode != noErr) {
        if(_EncodingSession != NULL) {
            NSLog(@"H264: VTCompressionSessionEncodeFrame failed with %d", (int)statusCode);
            VTCompressionSessionInvalidate(_EncodingSession);
            CFRelease(_EncodingSession);
            _EncodingSession = NULL;
            NSLog(@"encodingSession release");
            return;
        }
    }
//    NSLog(@"H264: VTCompressionSessionEncodeFrame Success");
}

5、在回撥函式中處理編碼後的H264資料

根據H264的編碼規範，我們需要先取出PPS和SPS資料儲存，然後再依次儲存H264的視訊資料

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;
    }
    ESCSaveToH264FileTool* encoder = (__bridge ESCSaveToH264FileTool *)outputCallbackRefCon;
    
    bool keyframe = !CFDictionaryContainsKey( (CFArrayGetValueAtIndex(CMSampleBufferGetSampleAttachmentsArray(sampleBuffer, true), 0)), kCMSampleAttachmentKey_NotSync);
    // 判斷當前幀是否為關鍵幀
    // 獲取sps & pps資料
    if (keyframe) {
        CMFormatDescriptionRef format = CMSampleBufferGetFormatDescription(sampleBuffer);
        size_t spsSize, spsCount;
        const uint8_t *sparameterSet;
        OSStatus statusCode = CMVideoFormatDescriptionGetH264ParameterSetAtIndex(format, 0, &sparameterSet, &spsSize, &spsCount, 0 );
        if (statusCode == noErr) {
            // Found sps and now check for pps
            size_t ppsSize, ppsCount;
            const uint8_t *pparameterSet;
            OSStatus statusCode = CMVideoFormatDescriptionGetH264ParameterSetAtIndex(format, 1, &pparameterSet, &ppsSize, &ppsCount, 0 );
            if (statusCode == noErr) {
                // Found pps
                NSData *sps = [NSData dataWithBytes:sparameterSet length:spsSize];
                NSData *pps = [NSData dataWithBytes:pparameterSet length:ppsSize];
                if (encoder) {
                    [encoder gotSpsPps:sps pps: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資料前四個位元組不是0001的startcode，而是大端模式的幀長度length
        
        // 迴圈獲取nalu資料
        while (bufferOffset < totalLength - AVCCHeaderLength) {
            uint32_t NALUnitLength = 0;
            // Read the NAL unit length
            memcpy(&NALUnitLength, dataPointer + bufferOffset, AVCCHeaderLength);
            
            // 從大端轉系統端
            NALUnitLength = CFSwapInt32BigToHost(NALUnitLength);
            
            NSData* data = [[NSData alloc] initWithBytes:(dataPointer + bufferOffset + AVCCHeaderLength) length:NALUnitLength];
            [encoder gotEncodedData:data isKeyFrame:keyframe];
            
            // Move to the next NAL unit in the block buffer
            bufferOffset += AVCCHeaderLength + NALUnitLength;
        }
    }
}

寫入SPS和PPS資訊

- (void)gotSpsPps:(NSData *)sps pps:(NSData *)pps {
//    NSLog(@"gotSpsPps %d %d", (int)[sps length], (int)[pps length]);
    const char bytes[] = "\x00\x00\x00\x01";
    NSData *ByteHeader = [NSData dataWithBytes:bytes length:4];
    [self.fileHandle writeData:ByteHeader];
    [self.fileHandle writeData:sps];
    [self.fileHandle writeData:ByteHeader];
    [self.fileHandle writeData:pps];
}

寫入H264裸資料

- (void)gotEncodedData:(NSData*)data isKeyFrame:(BOOL)isKeyFrame {
//    NSLog(@"gotEncodedData %d", (int)[data length]);
    if (self.fileHandle != 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];
        [self.fileHandle writeData:ByteHeader];
        [self.fileHandle writeData:data];
    }
}

6、結束錄製時停止編碼會話和視訊流會話

停止編碼會話

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

停止視訊會話

[self.captureSession stopRunning];

結束視訊的錄製。我們開啟沙盒即可檢視錄製的H264檔案。
可以使用VLC進行播放。

最後歡迎大家留言交流，同時附上Demo地址。
Demo地址：https://github.com/XMSECODE/ESCCameraToH264Demo

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