How to change AVCaptureMovieFileOutput video orientation during running session?

Question

I have made a code that captures device video input and so far it is working fine. Here is what I have set

// 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];

where:

- (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;
        }
    }
}

Now when interface orientation changes I want my output also to change, so I have this:

- (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];
}

But alas it is not working. It seems once I first set video orientation on movie output, it stays like than, it can not be changed later. So if I start filming in landscape mode, and then change to portrait, the video will be ok for the landscape mode, but portrait mode will be rotated. It is the same if I start in portrait mode, than landscape will be rotated.

Is there any way to do this right?

Answer 1

Try adding this before you start your session:

[_movieFileOutput setRecordsVideoOrientationAndMirroringChanges:YES asMetadataTrackForConnection:movieFileOutputConnection];

The header file documentation for this method makes it sound very much like what you're looking for:

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.

There's more interesting information there, I'd read it all.

However, this method doesn't actually rotate your frames, it uses timed metadata to instruct players to do it at playback time, so it's possible that not all players will support this feature. If that's a deal breaker, then you can abandon AVCaptureMovieFileOutput in favour of the lower level AVCaptureVideoDataOutput + AVAssetWriter combination, where your videoOrientation changes actually rotate the frames, resulting in files that will playback correctly in any player:

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.