如何在运行会话期间更改AVCaptureMovieFileOutput视频方向？

Question

我已经制作了一个捕获设备视频输入的代码,到目前为止它工作正常.这是我设定的

// add preview layer
_previewLayer = [AVCaptureVideoPreviewLayer layerWithSession:_session];
_previewLayer.videoGravity = AVLayerVideoGravityResizeAspectFill;
[self.videoView.layer addSublayer:_previewLayer];

// add movie output
_movieFileOutput = [[AVCaptureMovieFileOutput alloc] init];
[_session addOutput:_movieFileOutput];
AVCaptureConnection *movieFileOutputConnection = [_movieFileOutput connectionWithMediaType:AVMediaTypeVideo];
movieFileOutputConnection.videoOrientation = [self videoOrientationFromCurrentDeviceOrientation];

// start session
[_session startRunning];

哪里:

- (AVCaptureVideoOrientation) videoOrientationFromCurrentDeviceOrientation {
    switch ([[UIApplication sharedApplication] statusBarOrientation]) {
        case UIInterfaceOrientationPortrait: {
            return AVCaptureVideoOrientationPortrait;
        }
        case UIInterfaceOrientationLandscapeLeft: {
            return AVCaptureVideoOrientationLandscapeLeft;
        }
        case UIInterfaceOrientationLandscapeRight: {
            return AVCaptureVideoOrientationLandscapeRight;
        }
        case UIInterfaceOrientationPortraitUpsideDown: {
            return AVCaptureVideoOrientationPortraitUpsideDown;
        }
        case UIInterfaceOrientationUnknown: {
            return 0;
        }
    }
}

现在,当界面方向改变时,我希望我的输出也改变,所以我有这个:

- (void) updatePreviewLayer {
    _previewLayer.frame = CGRectMake(0, 0, self.videoView.frame.size.width, self.videoView.frame.size.height);
    _previewLayer.connection.videoOrientation = [self videoOrientationFromCurrentDeviceOrientation];
    [_session beginConfiguration];
    AVCaptureConnection *movieFileOutpurConnection = [_movieFileOutput connectionWithMediaType:AVMediaTypeVideo];
    movieFileOutpurConnection.videoOrientation = [self videoOrientationFromCurrentDeviceOrientation];
    [_session commitConfiguration];
}

但唉,它不起作用.似乎有一次我首先在电影输出上设置视频方向,它保持不变,以后不能更改.因此,如果我开始以横向模式拍摄,然后更改为肖像,视频将适用于横向模式,但纵向模式将会旋转.如果我以纵向模式开始,则会旋转景观.

有没有办法做到这一点？

Answer 1

尝试在开始会话之前添加此内容：

[_movieFileOutput setRecordsVideoOrientationAndMirroringChanges:YES asMetadataTrackForConnection:movieFileOutputConnection];

此方法的头文件文档使其听起来非常像您正在寻找的内容：

控制影片文件输出是否创建定时元数据轨道，该轨道记录反映录制期间对给定连接的 videoOrientation 和 videoMirrored 属性所做更改的示例。

那里有更多有趣的信息，我会全部阅读。

但是，此方法实际上并不旋转帧，它使用定时元数据来指示播放器在播放时执行此操作，因此可能并非所有播放器都支持此功能。如果这是一个破坏因素，那么您可以放弃AVCaptureMovieFileOutput，转而选择较低级别 AVCaptureVideoDataOutput+AVAssetWriter组合，您的videoOrientation更改实际上会旋转帧，从而生成可以在任何播放器中正确播放的文件：

If an AVCaptureVideoDataOutput instance's connection's videoOrientation or videoMirrored properties are set to non-default values, the output applies the desired mirroring and orientation by physically rotating and or flipping sample buffers as they pass through it.

p.s. I don't think you need the beginConfiguration/commitConfiguration pair if you're only changing one property as that's for batching multiple modifications into one atomic update.