Ich nehme das Video mit UIImagePickerController auf. Ich kann das Video mit folgendem Code zuschneiden:

AVAsset *asset = [AVAsset assetWithURL:url];

//create an avassetrack with our asset
AVAssetTrack *clipVideoTrack = [[asset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0];

//create a video composition and preset some settings
AVMutableVideoComposition* videoComposition = [AVMutableVideoComposition videoComposition];
videoComposition.frameDuration = CMTimeMake(1, 30);
//here we are setting its render size to its height x height (Square)

videoComposition.renderSize = CGSizeMake(clipVideoTrack.naturalSize.height, clipVideoTrack.naturalSize.height);

//create a video instruction
AVMutableVideoCompositionInstruction *instruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction];
instruction.timeRange = CMTimeRangeMake(kCMTimeZero, CMTimeMakeWithSeconds(60, 30));

AVMutableVideoCompositionLayerInstruction* transformer = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:clipVideoTrack];

//Here we shift the viewing square up to the TOP of the video so we only see the top
CGAffineTransform t1 = CGAffineTransformMakeTranslation(clipVideoTrack.naturalSize.height, -20);

//Use this code if you want the viewing square to be in the middle of the video
//CGAffineTransform t1 = CGAffineTransformMakeTranslation(clipVideoTrack.naturalSize.height, -(clipVideoTrack.naturalSize.width - clipVideoTrack.naturalSize.height) /2 );

//Make sure the square is portrait
CGAffineTransform t2 = CGAffineTransformRotate(t1, M_PI_2);

CGAffineTransform finalTransform = t2;
[transformer setTransform:finalTransform atTime:kCMTimeZero];

//add the transformer layer instructions, then add to video composition
instruction.layerInstructions = [NSArray arrayWithObject:transformer];
videoComposition.instructions = [NSArray arrayWithObject: instruction];

//Create an Export Path to store the cropped video
NSString *outputPath = [NSString stringWithFormat:@"%@%@", NSTemporaryDirectory(), @"video.mp4"];
NSURL *exportUrl = [NSURL fileURLWithPath:outputPath];

//Remove any prevouis videos at that path
[[NSFileManager defaultManager]  removeItemAtURL:exportUrl error:nil];

//Export    
AVAssetExportSession *exporter = [[AVAssetExportSession alloc] initWithAsset:asset presetName:AVAssetExportPresetLowQuality] ;
exporter.videoComposition = videoComposition;
exporter.outputURL = exportUrl;
exporter.outputFileType = AVFileTypeMPEG4;

[exporter exportAsynchronouslyWithCompletionHandler:^
 {
     dispatch_async(dispatch_get_main_queue(), ^{
         //Call when finished
         [self exportDidFinish:exporter];
     });
 }];

Aber ich weiß nicht, wie ich das Orientierungsproblem beheben soll. Wie bei der App instagram und vine (d. H.) Sollte sich das Video im Hochformat befinden, wenn ich es auch im Querformat aufnehme, und das Video als Quadrat zuschneiden müssen. Bitte geben Sie mir die Lösung ... Ich habe Probleme mit diesem Problem ...