问题
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?
回答1:
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;
}
回答2:
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
回答3:
AVAssetImageGenerator
If you are using AVAssetImageGenerator to generate images from AVAssets, you can simply set the .appliesPreferredTrackTransform property of AVAssetImageGenerator to true and it will return you images from your asset in the correct orientation! :)
Swift 3
But to extend on @onmyway133's answer in Swift 3:
import UIKit
import AVFoundation
extension AVAsset {
var g_size: CGSize {
return tracks(withMediaType: AVMediaTypeVideo).first?.naturalSize ?? .zero
}
var g_orientation: UIInterfaceOrientation {
guard let transform = tracks(withMediaType: AVMediaTypeVideo).first?.preferredTransform else {
return .portrait
}
switch (transform.tx, transform.ty) {
case (0, 0):
return .landscapeRight
case (g_size.width, g_size.height):
return .landscapeLeft
case (0, g_size.width):
return .portraitUpsideDown
default:
return .portrait
}
}
}
回答4:
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.
回答5:
If you do not want to use AVFoundation Framework just to get the orientation of the recorded video then try it out
-(void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo: (NSDictionary *)info {
NSString *orientation;
NSString *videoPath = [[info objectForKey:UIImagePickerControllerMediaURL] path];
NSURL *myURL = [[NSURL alloc] initFileURLWithPath:videoPath];
self.movieController = [[MPMoviePlayerController alloc] initWithContentURL:myURL];
UIImage *thumbImage = [movieController thumbnailImageAtTime:1.0 timeOption:MPMovieTimeOptionNearestKeyFrame];
float width = thumbImage.size.width;
float height = thumbImage.size.height;
if (width > height){
orientation = @"Landscape";
}else{
orientation = @"Portrait";
}
[self dismissViewControllerAnimated:YES completion:nil];
}
回答6:
While several of the answers here are correct, they are not comprehensive. For instance, you may also need to know which camera device was used to apply the proper transforms. I created a gist to do this very thing; extract the UIInterfaceOrientation and the AVCaptureDevicePosition.
Extract AVAsset Orientation and Camera Position
回答7:
- (UIImageOrientation)getImageOrientationWithVideoOrientation:(UIInterfaceOrientation)videoOrientation {
UIImageOrientation imageOrientation;
switch (videoOrientation) {
case UIInterfaceOrientationLandscapeLeft:
imageOrientation = UIImageOrientationUp;
break;
case UIInterfaceOrientationLandscapeRight:
imageOrientation = UIImageOrientationDown;
break;
case UIInterfaceOrientationPortrait:
imageOrientation = UIImageOrientationRight;
break;
case UIInterfaceOrientationPortraitUpsideDown:
imageOrientation = UIImageOrientationLeft;
break;
}
return imageOrientation;
}
回答8:
Extending on George's answer in Swift 2
UIInterfaceOrientation is the same with UIImageOrientation
extension AVAsset {
var g_size: CGSize {
return tracksWithMediaType(AVMediaTypeVideo).first?.naturalSize ?? .zero
}
var g_orientation: UIInterfaceOrientation {
guard let transform = tracksWithMediaType(AVMediaTypeVideo).first?.preferredTransform else {
return .Portrait
}
switch (transform.tx, transform.ty) {
case (0, 0):
return .LandscapeRight
case (g_size.width, g_size.height):
return .LandscapeLeft
case (0, g_size.width):
return .PortraitUpsideDown
default:
return .Portrait
}
}
}
来源：https://stackoverflow.com/questions/4627940/how-to-detect-if-a-video-file-was-recorded-in-portrait-orientation-or-landscape