ios - 如何在运行 session 期间更改 AVCaptureMovieFileOutput 视频方向？

Question

我已经编写了一个捕获设备视频输入的代码，到目前为止它运行良好。这是我设置的

// 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];

地点:

- (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];
}

但是，可惜它不起作用。似乎一旦我第一次在电影输出上设置视频方向，它就会保持不变，以后无法更改。因此，如果我开始以横向模式拍摄，然后更改为纵向模式，则视频在横向模式下没问题，但纵向模式会旋转。如果我以纵向模式开始也是一样的，横向将被旋转。

有什么办法可以做到这一点吗？

Answer 1

尝试在开始 session 之前添加:

[_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:

Controls whether or not the movie file output will create a timed metadata track that records samples which reflect changes made to the given connection's videoOrientation and videoMirrored properties during recording.

那里有更多有趣的信息，我会全部阅读。

但是，此方法实际上并不会旋转您的帧，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。如果这是一个交易破坏者，那么你可以放弃 AVCaptureMovieFileOutput 支持较低级别的 AVCaptureVideoDataOutput + AVAssetWriter 组合，其中你的 videoOrientation 更改实际上旋转了帧，导致文件可以在任何播放器中正确播放:

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.

附注如果您只更改一个属性，我认为您不需要 beginConfiguration/commitConfiguration 对，因为这是将多个修改批处理到一个原子更新中。