iOS 视频采集

前言

AVFoundation框架是iOS中很重要的框架，所有与音视频相关的软硬件控制都在这个框架里。本文主要介绍iOS媒体捕捉和视频采集。

媒体捕捉流程

媒体捕捉(网侵删).png

简单介绍

• AVCaptureSession：媒体捕获会话（包括音频和视频），负责把捕获的音视频数据输出到输出设备中，一个AVCaptureSession可以有多个输入输出。
  在视频或音频捕捉时，客户端可以实例AVCaptureSession，添加适当的AVCaptureInputs、AVCaptureDeviceInput和输出。
• AVCaptureInput和AVCaptureDevice：设备输入数据管理对象，可以根据AVCaptureDevice创建对应AVCaptureDeviceInput对象，该对象将会被添加到AVCaptureSession中管理。
• AVCaptureOutput：设备输出数据管理对象。
• AVCaptureVideoPreviewLayer和AVSampleBufferDisplayLayer，相机拍摄预览图层，是CALayer的子类，前者创建需要AVCaptureSession对象，后者可以直接创建，添加CMSampleBufferRef进行展示。

相关代码展示

- (void)configureCamera{
    /// 参数设置
    // 默认后置摄像头
    AVCaptureDevicePosition position = AVCaptureDevicePositionBack;
    // 帧率
    int frameRate = 25;
    // 显色方案
    OSType videoFormat = kCVPixelFormatType_32BGRA;
    // 分辨率高
    int resolutionHeight = 720;
    
    /// 创建AVCaptureSession对象
    AVCaptureSession *session = [[AVCaptureSession alloc] init];
    /// 设置分辨率
    session.sessionPreset = AVCaptureSessionPreset1280x720;
    /// 获取摄像头
    AVCaptureDevice *captureDevice;
    // 默认AVCaptureDevicePositionBack，后置摄像头
    AVCaptureDeviceDiscoverySession *deviceDiscoverySession =  [AVCaptureDeviceDiscoverySession discoverySessionWithDeviceTypes:@[AVCaptureDeviceTypeBuiltInWideAngleCamera] mediaType:AVMediaTypeVideo position:position];
    NSArray *devices = deviceDiscoverySession.devices;
    for (AVCaptureDevice *device in devices) {
        if (AVCaptureDevicePositionBack == device.position) {
            captureDevice = device;
        }else if (AVCaptureDevicePositionFront == device.position){
            captureDevice = device;
        }
    }
    /// 设置帧率和分辨率高度
    BOOL isSuccess = NO;
    for(AVCaptureDeviceFormat *vFormat in [captureDevice formats]) {
        CMFormatDescriptionRef description = vFormat.formatDescription;
        float maxRate = ((AVFrameRateRange*) [vFormat.videoSupportedFrameRateRanges objectAtIndex:0]).maxFrameRate;
        if (maxRate >= frameRate && CMFormatDescriptionGetMediaSubType(description) == videoFormat) {
            if ([captureDevice lockForConfiguration:NULL] == YES) {
                // 对比镜头支持的分辨率和当前设置的分辨率
                CMVideoDimensions dims = CMVideoFormatDescriptionGetDimensions(description);
                if (dims.height == resolutionHeight && dims.width == [self.class getResolutionWidthByHeight:resolutionHeight]) {
                    [session beginConfiguration];
                    if ([captureDevice lockForConfiguration:NULL]){
                        captureDevice.activeFormat = vFormat;
                        [captureDevice setActiveVideoMinFrameDuration:CMTimeMake(1, frameRate)];
                        [captureDevice setActiveVideoMaxFrameDuration:CMTimeMake(1, frameRate)];
                        [captureDevice unlockForConfiguration];
                    }
                    [session commitConfiguration];
                    isSuccess = YES;
                }
            }else {
                NSLog(@"%s: 失败",__func__);
            }
        }
    }
    
    NSError *error;
    
    //添加输入
    AVCaptureDeviceInput *input = [AVCaptureDeviceInput deviceInputWithDevice:captureDevice error:&error];
    if (error != noErr) {
        NSLog(@"配置设备输入失败:%@",error.localizedDescription);
        return;
    }
    [session addInput:input];
    
    //添加输出
    AVCaptureVideoDataOutput *videoDataOutput = [[AVCaptureVideoDataOutput alloc] init];
    if ([session canAddOutput:videoDataOutput]) {
        [session addOutput:videoDataOutput];
    }
    videoDataOutput.videoSettings = [NSDictionary dictionaryWithObject:[NSNumber numberWithInt:videoFormat]
                                                                forKey:(id)kCVPixelBufferPixelFormatTypeKey];
    //当此属性的值为YES时，接收方将立即丢弃捕获的帧，而处理现有帧的调度队列在captureOutput:didOutputSampleBuffer:fromConnection: delegate方法中被阻塞。当此属性的值为NO时，将允许委托在丢弃新帧之前有更多的时间处理旧帧，但应用程序的内存使用量可能会显著增加。默认值为“YES”。（机翻）
    videoDataOutput.alwaysDiscardsLateVideoFrames = NO;
    
    //创建一个队列接收数据
    dispatch_queue_t videoQueue = dispatch_queue_create("video_receive_queue", NULL);
    [videoDataOutput setSampleBufferDelegate:self queue:videoQueue];
    
    //创建接收对象
    AVCaptureVideoPreviewLayer *videoPreviewLayer = [[AVCaptureVideoPreviewLayer alloc] initWithSession:session];
    videoPreviewLayer.backgroundColor = [[UIColor blackColor] CGColor];
    CGRect frame = [videoPreviewLayer bounds];
    NSLog(@"previewViewLayer = %@",NSStringFromCGRect(frame));
    
    //设置尺寸和填充方式
    [videoPreviewLayer setFrame:[UIScreen mainScreen].bounds];
    [videoPreviewLayer setVideoGravity:AVLayerVideoGravityResizeAspect];
    
    if ([[videoPreviewLayer connection] isVideoOrientationSupported]) {
        [videoPreviewLayer.connection setVideoOrientation:AVCaptureVideoOrientationPortrait];
    }else{
        NSLog(@"不支持视频定向");
    }
    
    //需要在哪个view上展示
    UIView *showView = [[UIView alloc] init];
    [showView.layer insertSublayer:videoPreviewLayer atIndex:0];
    
}
//采集视频的回调，如果需要编码H264/H265,在这里操作
- (void)captureOutput:(AVCaptureOutput *)output didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection{
    /*
    //另一种展示方式
    AVSampleBufferDisplayLayer *previewLayer = [AVSampleBufferDisplayLayer layer];
    previewLayer.videoGravity =  AVLayerVideoGravityResizeAspectFill;
    [previewLayer enqueueSampleBuffer:sampleBuffer];
    //需要在哪个view上展示
    UIView *showView = [[UIView alloc] init];
    [showView.layer insertSublayer:previewLayer atIndex:0];
     */
}
///需要考虑横竖屏情况，这里暂未考虑
+ (int)getResolutionWidthByHeight:(int)height {
    switch (height) {
        case 2160:
            return 3840;
        case 1080:
            return 1920;
        case 720:
            return 1280;
        case 480:
            return 640;
        default:
            return -1;
    }
}

Tips：配置采集之前，记得申请摄像头权限，如果没有权限，需要自己做判断，这里省略。
Demo地址整理后奉上。
有其他不明白的，可以留言，看到就会回复。
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