iPhone 摄像头在纵向模式下产生的这些额外字节是什么？

Question

当我从 - (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection 得到一帧时，我得到了以下数据：

每行字节数：1,472 长度：706,560 高度：480 宽度：360 格式： BGRA

这是来自 iPhone 6 plus 的前置摄像头。这没有意义，因为每行的字节数应该是 (width * channels)（在这种情况下，channels 是 4）。但是，它是 (width+8)*channels。这额外的 8 个字节来自哪里？

这是我的代码：将输出附加到会话，我将方向设置为纵向

bool attachOutputToSession(AVCaptureSession *session, id cameraDelegate)
{
    assert(cameraDelegate);

    AVCaptureVideoDataOutput *m_videoOutput = [[AVCaptureVideoDataOutput alloc] init];

    //create a queue for capturing frames
    dispatch_queue_t captureQueue  = dispatch_queue_create("captureQueue", DISPATCH_QUEUE_SERIAL);

    //Use the AVCaptureVideoDataOutputSampleBufferDelegate capabilities of CameraDelegate:
    [m_videoOutput setSampleBufferDelegate:cameraDelegate queue:captureQueue];

    //setup the video outputs
    m_videoOutput.alwaysDiscardsLateVideoFrames = YES;

    NSNumber *framePixelFormat = [NSNumber numberWithInt:kCVPixelFormatType_32BGRA];//This crashes with 24RGB b/c that isn't supported on iPhone
    m_videoOutput.videoSettings = [ NSDictionary dictionaryWithObject:framePixelFormat forKey:(id)kCVPixelBufferPixelFormatTypeKey];

    //Check if it already has an output from a previous session
    if ([session canAddOutput:m_videoOutput])
    {
        [session addOutput:m_videoOutput];
    }

    //set connection settings
    for (AVCaptureConnection *connection in m_videoOutput.connections)
    {
        if (connection.isVideoMirroringSupported)
            connection.videoMirrored = true;
        if (connection.isVideoOrientationSupported)
            connection.videoOrientation = AVCaptureVideoOrientationPortrait; 
    }

    return true;
}

当我将方向设置为 LandscapeRight 时，我没有遇到这个问题。每行的字节等于宽度*通道。

这是我获取上述数字的地方：

-(void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection
{
    CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer);

    CIImage *ciImage = [CIImage imageWithCVPixelBuffer:imageBuffer];

    CVPixelBufferLockBaseAddress(imageBuffer,0);
    size_t bytesPerRow = CVPixelBufferGetBytesPerRow(imageBuffer);
    size_t width = CVPixelBufferGetWidth(imageBuffer);
    size_t height = CVPixelBufferGetHeight(imageBuffer);
}

Answer 1

确定这是图像的一部分 "stride"。如果图像宽度不能被所选的内存分配整除，则包括此额外填充。当我收到肖像图像时，它是 360x480。由于 360 不能被 16 整除，因此添加 8 个额外字节作为填充。在这种情况下，16 是内存 space。我以前没有遇到过这个问题，因为 480 可以被 16 整除。您可以拨打 CVPixelBufferGetBytesPerRowOfPlane (imageBuffer, 1); 获取此号码但奇怪的是，它 returns 第一次为 0，第二次为 1，依此类推，直到达到实际缓冲区级别 (8)。然后在第九张图片上再次 returns 0 。

根据此页面上的 rpappalax http://gstreamer-devel.966125.n4.nabble.com/iOS-capture-problem-td4656685.html

The stride is effectively CVPixelBufferGetBytesPerRowOfPlane() and includes padding (if any). When no padding is present CVPixelBufferGetBytesPerRowOfPlane() will be equal to CVPixelBufferGetWidth(), otherwise it'll be greater.

虽然那不是我的经验。

iPhone 摄像头在纵向模式下产生的这些额外字节是什么？

What are these extra bytes coming from the iPhone camera in portrait mode?

iphone

ios8

avfoundation

avcapturesession