I am using AlAssetsGroup enumerateAssetsAtIndexes to list the assets in the Photos (Camera) app. For a given video asset I want to determine whether it was shot in portrait or landscape mode.
In the following code, asset is an AlAsset and I have tested to see if it is a video asset [asset valueForProperty:ALAssetPropertyType] is AlAssetTypeVideo, then:
int orientation = [[asset valueForProperty:ALAssetPropertyOrientation] intValue];
In this case orientation is always 0 which is ALAssetOrientationUp. Maybe this is to be expected, all videos are up right, but a portrait video is represented in MPEG-4 as a landscape video turned 90 degrees (i.e. all videos are actually landscape, try the MediaInfo app on the mac if you don't believe me).
Where within the file and/or how do I access the information that tells me it was actually recorded while holding the phone in portrait orientation?
I have also tried this, given the url of the asset:
AVURLAsset *avAsset = [[AVURLAsset alloc] initWithURL:url options:nil];
CGSize size = [avAsset naturalSize];
NSLog(@"size.width = %f size.height = %f", size.width, size.height);
CGAffineTransform txf = [avAsset 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);
Which always yields a width > height so for iPhone 4, width=1280 height=720 and the transform a and d values are 1.0, the others are 0.0, regardless of the capture orientation.
I have looked at the meta data using MediaInfo app on the Mac, I have done a Hexdump and so far have not found any difference between a landscape and portrait video. But QuickTime knows and displays portrait videos vertically, and the phone knows by rotating a portrait video if you are holding the phone in landscape orientation on playback and correctly displaying it if holding it in portrait.
BTW I can't use ffmpeg (can't live with the license restrictions). Is there an iPhone SDK native way to do this?
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)
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
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 = 0.0000002011-01-07 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 = 1280.0000002011-01-07 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