拍摄照片时切换AVCaptureSession预设

Question

我目前的设置如下(基于Brad Larson的ColorTrackingCamera项目):

我正在使用一个AVCaptureSession集合AVCaptureSessionPreset640x480,我让输出通过OpenGL场景作为纹理运行.然后由片段着色器操纵该纹理.

我需要这种"低质量"预设,因为我想在用户预览时保持高帧率.然后我想在用户拍摄静态照片时切换到更高质量的输出.

首先,我认为我可以改变它sessionPreset,AVCaptureSession但这会迫使相机重新聚焦,这会破坏可用性.

[captureSession beginConfiguration];
captureSession.sessionPreset = AVCaptureSessionPresetPhoto;
[captureSession commitConfiguration];

目前我正在尝试向AVCaptureStillImageOutputAVCaptureSession 添加第二个,但我得到一个空像素缓冲,所以我觉得我有点卡住了.

这是我的会话设置代码:

...

// Add the video frame output
[captureSession beginConfiguration];

videoOutput = [[AVCaptureVideoDataOutput alloc] init];
[videoOutput setAlwaysDiscardsLateVideoFrames:YES];
[videoOutput setVideoSettings:[NSDictionary dictionaryWithObject:[NSNumber numberWithInt:kCVPixelFormatType_32BGRA] forKey:(id)kCVPixelBufferPixelFormatTypeKey]];
[videoOutput setSampleBufferDelegate:self queue:dispatch_get_main_queue()];

if ([captureSession canAddOutput:videoOutput])
{
    [captureSession addOutput:videoOutput];
}
else
{
    NSLog(@"Couldn't add video output");
}

[captureSession commitConfiguration];



// Add still output
[captureSession beginConfiguration];
stillOutput = [[AVCaptureStillImageOutput alloc] init];

if([captureSession canAddOutput:stillOutput])
{
    [captureSession addOutput:stillOutput];
}
else
{
    NSLog(@"Couldn't add still output");
}

[captureSession commitConfiguration];



// Start capturing
[captureSession setSessionPreset:AVCaptureSessionPreset640x480];
if(![captureSession isRunning])
{
    [captureSession startRunning];
};

...

这是我的捕获方法:

- (void)prepareForHighResolutionOutput
{
    AVCaptureConnection *videoConnection = nil;
    for (AVCaptureConnection *connection in stillOutput.connections) {
        for (AVCaptureInputPort *port in [connection inputPorts]) {
            if ([[port mediaType] isEqual:AVMediaTypeVideo] ) {
                videoConnection = connection;
                break;
            }
        }
        if (videoConnection) { break; }
    }

    [stillOutput captureStillImageAsynchronouslyFromConnection:videoConnection completionHandler:
     ^(CMSampleBufferRef imageSampleBuffer, NSError *error) {
         CVImageBufferRef pixelBuffer = CMSampleBufferGetImageBuffer(imageSampleBuffer);
         CVPixelBufferLockBaseAddress(pixelBuffer, 0);
         int width = CVPixelBufferGetWidth(pixelBuffer);
         int height = CVPixelBufferGetHeight(pixelBuffer);

         NSLog(@"%i x %i", width, height);
         CVPixelBufferUnlockBaseAddress(pixelBuffer, 0);
     }];
}

(width并height变成是0)

我已经阅读了AVFoundation文档的文档,但似乎我没有得到必要的东西.

Answer 1

我找到了针对我的具体问题的解决方案。如果有人偶然发现同样的问题，我希望它可以用作指南。

帧率大幅下降的原因与像素格式之间的内部转换有关。明确设置像素格式后，帧速率增加。

在我的情况下，我使用以下方法创建 BGRA 纹理：

// Let Core Video create the OpenGL texture from pixelbuffer
CVReturn err = CVOpenGLESTextureCacheCreateTextureFromImage(kCFAllocatorDefault, videoTextureCache, pixelBuffer, NULL,
                                                            GL_TEXTURE_2D, GL_RGBA, width, height, GL_BGRA,
                                                            GL_UNSIGNED_BYTE, 0, &videoTexture);

因此，当我设置AVCaptureStillImageOutput实例时，我将代码更改为：

// Add still output
stillOutput = [[AVCaptureStillImageOutput alloc] init];
[stillOutput setOutputSettings:[NSDictionary dictionaryWithObject:[NSNumber numberWithInt:kCVPixelFormatType_32BGRA] forKey:(id)kCVPixelBufferPixelFormatTypeKey]];

if([captureSession canAddOutput:stillOutput])
{
    [captureSession addOutput:stillOutput];
}
else
{
    NSLog(@"Couldn't add still output");
}

我希望这有一天能帮助别人；）