How to detect if a video file was recorded in portrait orientation, or landscape in iOS

Based on the previous answer, you can use the following to determine the video orientation:

+ (UIInterfaceOrientation)orientationForTrack:(AVAsset *)asset
{
    AVAssetTrack *videoTrack = [[asset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0];
    CGSize size = [videoTrack naturalSize];
    CGAffineTransform txf = [videoTrack preferredTransform];

    if (size.width == txf.tx && size.height == txf.ty)
        return UIInterfaceOrientationLandscapeRight;
    else if (txf.tx == 0 && txf.ty == 0)
        return UIInterfaceOrientationLandscapeLeft;
    else if (txf.tx == 0 && txf.ty == size.width)
        return UIInterfaceOrientationPortraitUpsideDown;
    else
        return UIInterfaceOrientationPortrait;
}

Somebody on apple dev forums suggested getting the transform of the video track, this does the job. You can see from the logs below that for these orientations the results make sense and our web developer is now able to rotate a variety of vids so they all match and composite them into one video.

AVAssetTrack* videoTrack = [[avAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0];
CGSize size = [videoTrack naturalSize];
NSLog(@"size.width = %f size.height = %f", size.width, size.height);
CGAffineTransform txf = [videoTrack preferredTransform];
NSLog(@"txf.a = %f txf.b = %f txf.c = %f txf.d = %f txf.tx = %f txf.ty = %f", txf.a, txf.b, txf.c, txf.d, txf.tx, txf.ty);

Logs using 4 iPhone 4 videos with the normal cam: (1) landscape cam on right side (home button on left) (2) landscape left (3) portrait upside-down (4) portrait up-right (home button at bottom)

1. 2011-01-07 20:07:30.024 MySecretApp[1442:307] size.width = 1280.000000 size.height = 720.000000 2011-01-07 20:07:30.027 MySecretApp[1442:307] txf.a = -1.000000 txf.b = 0.000000 txf.c = 0.000000 txf.d = -1.000000 txf.tx = 1280.000000 txf.ty = 720.000000

2. 2011-01-07 20:07:45.052 MySecretApp[1442:307] size.width = 1280.000000 size.height = 720.000000 2011-01-07 20:07:45.056 MySecretApp[1442:307] txf.a = 1.000000 txf.b = 0.000000 txf.c = 0.000000
   txf.d = 1.000000 txf.tx = 0.000000
   txf.ty = 0.000000

3. 2011-01-07 20:07:53.763 MySecretApp[1442:307] size.width = 1280.000000 size.height = 720.000000 2011-01-07 20:07:53.766 MySecretApp[1442:307] txf.a = 0.000000 txf.b = -1.000000 txf.c = 1.000000
   txf.d = 0.000000 txf.tx = 0.000000 txf.ty = 1280.000000

4. 2011-01-07 20:08:03.490 MySecretApp[1442:307] size.width = 1280.000000 size.height = 720.000000 2011-01-07 20:08:03.493 MySecretApp[1442:307] txf.a = 0.000000 txf.b = 1.000000 txf.c = -1.000000
   txf.d = 0.000000 txf.tx = 720.000000 txf.ty = 0.000000

In my use case I only needed to know if a video is in portrait or not (landscape).

guard let videoTrack = AVAsset(url: videoURL).tracks(withMediaType: AVMediaTypeVideo).first else {
    return ...
}

let transformedVideoSize = videoTrack.naturalSize.applying(videoTrack.preferredTransform)
let videoIsPortrait = abs(transformedVideoSize.width) < abs(transformedVideoSize.height)

This has been tested with both front and rear cameras for all orientation possibilities.