Question

所以在我的应用程序中，我正在录制视频。我想将录制视频的fps限制为15 fps，因为速度更快，我处理每一帧都有问题。该应用程序的目标是iOS 5.0+，因此我不必担心iOS的旧版本。

我知道要设置最大fps，我可以使用AVCaptureConnection的setVideoMinFrameDuration。我也知道为了让它实际工作，我还必须setVideoMaxFrameDuration。但是，似乎在我的iPad上，AVCaptureConnection的isVideoMinFrameDurationSupported总是返回false，因此我从不设置videoMinFrameDuration，最终不得不回退到设置AVCAptureVideoDataOutput的minFrameDuration（这是一个不推荐的调用，并导致警告等等。谁能解释为什么我无法设置videoMinFrameDuration？

代码：

AVCaptureVideoDataOutput *videoDataOut = [[AVCaptureVideoDataOutput alloc] init];
NSDictionary *settings = [[NSDictionary alloc]
                                        initWithObjectsAndKeys:[NSNumber numberWithUnsignedInt:kCVPixelFormatType_420YpCbCr8BiPlanarFullRange],
                                        (id)kCVPixelBufferPixelFormatTypeKey, nil];
videoDataOut.videoSettings = settings;

captureQueue = dispatch_queue_create("videoCaptureQueue", NULL);
    [videoDataOut setSampleBufferDelegate:self queue:captureQueue];
    videoDataOut.alwaysDiscardsLateVideoFrames = YES;
    AVCaptureConnection *conn = [videoDataOut connectionWithMediaType:AVMediaTypeVideo];

    // This if block is failing for some reason even though I'm running iOS 5.0+
    if ([conn isVideoMinFrameDurationSupported] && [conn isVideoMaxFrameDurationSupported]){
        [conn setVideoMinFrameDuration:CMTimeMake(1, pParams->fps)];
        [conn setVideoMaxFrameDuration:CMTimeMake(1, pParams->fps)];
    }
    else {
        videoDataOut.minFrameDuration = CMTimeMake(1, pParams->fps);
    }
    [captureSession addOutput:videoDataOut];

dispatch_release(captureQueue);

Answer 1

我想出了我的问题。在尝试设置minFrameDuration之前，你必须将输出添加到捕获会话中（或者，就此而言，拉出AVCaptureConnection）。

所以，新代码看起来像这样：

AVCaptureVideoDataOutput *videoDataOut = [[AVCaptureVideoDataOutput alloc] init];
NSDictionary *settings = [[NSDictionary alloc]
                                        initWithObjectsAndKeys:[NSNumber numberWithUnsignedInt:kCVPixelFormatType_420YpCbCr8BiPlanarFullRange],
                                        (id)kCVPixelBufferPixelFormatTypeKey, nil];
videoDataOut.videoSettings = settings;

captureQueue = dispatch_queue_create("videoCaptureQueue", NULL);
[videoDataOut setSampleBufferDelegate:self queue:captureQueue];
videoDataOut.alwaysDiscardsLateVideoFrames = YES;
[captureSession addOutput:videoDataOut];

AVCaptureConnection *conn = [videoDataOut connectionWithMediaType:AVMediaTypeVideo];
if ([conn isVideoMinFrameDurationSupported] && [conn isVideoMaxFrameDurationSupported]){
        [conn setVideoMinFrameDuration:CMTimeMake(1, pParams->fps)];
        [conn setVideoMaxFrameDuration:CMTimeMake(1, pParams->fps)];
}

dispatch_release(captureQueue);

AVCaptureConnection isVideoMinFrameDurationSupported是假的？

1 个答案: