相机采集

iOS系统相机氛围AVCaptureSession和AVCaptureMultiCamSession两种。主要区别是AVCaptureSession只能有一路的dataOuput,在多路输出的场景就需要使用AVCaptureMultiCamSession。

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初始化session

self.captureSession = [[AVCaptureSession alloc] init]; 

初始化device

- (AVCaptureDevice *)p_chooseBestDevice:(AVCaptureDevicePosition)pos deviceType:(NSArray<AVCaptureDeviceType> *)devieTypes {
    AVCaptureDevice *bestDevice;
    if (@available(iOS 10.0, *)) {
        if (devieTypes.count <0) {
            devieTypes = @[AVCaptureDeviceTypeBuiltInWideAngleCamera];
        }
        AVCaptureDeviceDiscoverySession *discorverySession = [AVCaptureDeviceDiscoverySession discoverySessionWithDeviceTypes:devieTypes mediaType:AVMediaTypeVideo position:pos];
        NSArray<AVCaptureDevice *> *devices = discorverySession.devices;
        for (AVCaptureDevice *device in devices) {
            for (AVCaptureDeviceType deviceType in devieTypes) {
                if ([deviceType isEqualToString:device.deviceType]) {
                    bestDevice = device;
                    break;
                }
            }
        }
    } else {
        NSArray<AVCaptureDevice *> *devices = [AVCaptureDevice devicesWithMediaType:AVMediaTypeVideo];
        for (AVCaptureDevice *device in devices) {
                if (device.position == pos) {
                    bestDevice = device;
                    break;
            }
        }
    }
    return bestDevice;
}

初始化input

self.deviceInput = [[AVCaptureDeviceInput alloc] initWithDevice:self.device error:&error];
    if (error) {
        ZZHDebugLog(@"%@", error);
    }
    if ([self.captureSession canAddInput:self.deviceInput]) {
        [self.captureSession addInput:self.deviceInput];
    }

初始化output

self.videoDataOutput = [[AVCaptureVideoDataOutput alloc] init];
    [self.videoDataOutput setAlwaysDiscardsLateVideoFrames:YES];
    [self.videoDataOutput setVideoSettings:[NSDictionary dictionaryWithObject:[NSNumber numberWithInt:kCVPixelFormatType_32BGRA] forKey:(id)kCVPixelBufferPixelFormatTypeKey]];

    self.videoCaptureQueue = dispatch_queue_create("com.zzh.videocatpure", 0);
    [self.videoDataOutput setSampleBufferDelegate:self queue:self.videoCaptureQueue];
    if ([self.captureSession canAddOutput:self.videoDataOutput]) {
        [self.captureSession addOutput:self.videoDataOutput];
    }

设置输出帧方向

AVCaptureConnection *connection = [self.videoDataOutput connectionWithMediaType:AVMediaTypeVideo];
    connection.videoOrientation = AVCaptureVideoOrientationPortrait;

AVCaptureVideoDataOutputSampleBufferDelegate

- (void)captureOutput:(AVCaptureOutput *)output didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection {
    if (output == self.videoDataOutput) {
        if (self.videoBufferCallBack) {
            self.videoBufferCallBack(sampleBuffer);
        }
    }
}
- (void)captureOutput:(AVCaptureOutput *)output didDropSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection API_AVAILABLE(ios(6.0), macCatalyst(14.0)) {
    ZZHDebugLog(@"");
}

metal上屏

初始化MTKView

- (void)p_initPreview:(CGRect)frame {
    self.preivew = [[MTKView alloc] initWithFrame:frame];
    self.preivew.device = MTLCreateSystemDefaultDevice();
    self.preivew.delegate = self;
    self.preivew.framebufferOnly = NO;
    self.commandQueue = [self.preivew.device newCommandQueue];
    CVMetalTextureCacheCreate(NULL, NULL, self.preivew.device, NULL, &_textureCache);
}

上传纹理

- (void)displayBuffer:(CMSampleBufferRef)buffer {
    CVPixelBufferRef pixelBuffer = CMSampleBufferGetImageBuffer(buffer);
    size_t width = CVPixelBufferGetWidth(pixelBuffer);
    size_t height = CVPixelBufferGetHeight(pixelBuffer);
    CVMetalTextureRef tmpTexture = NULL;
    CVReturn status = CVMetalTextureCacheCreateTextureFromImage(kCFAllocatorDefault, self.textureCache, pixelBuffer, NULL, MTLPixelFormatBGRA8Unorm, width, height, 0, &tmpTexture);
    if (status == kCVReturnSuccess) {
        self.preivew.drawableSize = CGSizeMake(width, height);
        self.texture = CVMetalTextureGetTexture(tmpTexture);
        CFRelease(tmpTexture);
    }
}

上屏

- (void)drawInMTKView:(nonnull MTKView *)view {
    if (self.texture) {
        id<MTLCommandBuffer> commandBuffer = [self.commandQueue commandBuffer];
        id<MTLTexture> drawingTexture = view.currentDrawable.texture;
        MPSImageGaussianBlur *filter = [[MPSImageGaussianBlur alloc] initWithDevice:view.device sigma:1];
        [filter encodeToCommandBuffer:commandBuffer sourceTexture:self.texture destinationTexture:drawingTexture];
        
        [commandBuffer presentDrawable:view.currentDrawable];
        [commandBuffer commit];
        self.texture = NULL;
    }
}

问题

1、activeFormat、preset留待后边讨论
2、输出帧数据格式的设置，有一些系统的行为，不设置、设置nil都有差别
3、输出帧的额外信息留待后边讨论，例如亮度
4、上屏的信息一定要和帧格式对齐，不然有色差，如转换矩阵、颜色空间等