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POVideo orientation issues when exporting with AVMutableVideoComposition
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copied!<p>Here is the function I used to export video:</p> <pre><code>- (void) videoOutput { //1 - Early exit if there's no video file selected if (!self.videoAsset) { UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Error" message:@"Please Load a Video Asset First" delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil]; [alert show]; return; } // 2 - Create AVMutableComposition object. This object will hold your AVMutableCompositionTrack instances. AVMutableComposition *mixComposition = [[AVMutableComposition alloc] init]; // 3 - Video track AVMutableCompositionTrack *videoTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid]; [videoTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, self.videoAsset.duration) ofTrack:[[self.videoAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0] atTime:kCMTimeZero error:nil]; // 3.1 - Create AVMutableVideoCompositionInstruction AVMutableVideoCompositionInstruction *mainInstruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction]; mainInstruction.timeRange = CMTimeRangeMake(kCMTimeZero, self.videoAsset.duration); // 3.2 - Create an AVMutableVideoCompositionLayerInstruction for the video track and fix the orientation. AVMutableVideoCompositionLayerInstruction *videolayerInstruction = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:videoTrack]; AVAssetTrack *videoAssetTrack = [[self.videoAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0]; BOOL isVideoAssetPortrait_ = NO; CGAffineTransform videoTransform = videoAssetTrack.preferredTransform; if (videoTransform.a == 0 && videoTransform.b == 1.0 && videoTransform.c == -1.0 && videoTransform.d == 0) { isVideoAssetPortrait_ = YES; } if (videoTransform.a == 0 && videoTransform.b == -1.0 && videoTransform.c == 1.0 && videoTransform.d == 0) { isVideoAssetPortrait_ = YES; } if (videoTransform.a == 1.0 && videoTransform.b == 0 && videoTransform.c == 0 && videoTransform.d == 1.0) { isVideoAssetPortrait_ = NO; } if (videoTransform.a == -1.0 && videoTransform.b == 0 && videoTransform.c == 0 && videoTransform.d == -1.0) { isVideoAssetPortrait_ = NO; } [videolayerInstruction setTransform:videoAssetTrack.preferredTransform atTime:kCMTimeZero]; [videolayerInstruction setOpacity:0.0 atTime:self.videoAsset.duration]; // 3.3 - Add instructions mainInstruction.layerInstructions = [NSArray arrayWithObjects:videolayerInstruction,nil]; AVMutableVideoComposition *mainCompositionInst = [AVMutableVideoComposition videoComposition]; CGSize naturalSize; if(isVideoAssetPortrait_){ naturalSize = CGSizeMake(videoAssetTrack.naturalSize.height, videoAssetTrack.naturalSize.width); } else { naturalSize = videoAssetTrack.naturalSize; } mainCompositionInst.renderSize = naturalSize; mainCompositionInst.instructions = [NSArray arrayWithObject:mainInstruction]; mainCompositionInst.frameDuration = CMTimeMake(1, 30); // 4 - Get path NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES); NSString *documentsDirectory = [paths objectAtIndex:0]; NSString *myPathDocs = [documentsDirectory stringByAppendingPathComponent: [NSString stringWithFormat:@"FinalVideo-%d.mov",arc4random() % 1000]]; NSURL *url = [NSURL fileURLWithPath:myPathDocs]; // 5 - Create exporter AVAssetExportSession *exporter = [[AVAssetExportSession alloc] initWithAsset:mixComposition presetName:AVAssetExportPresetHighestQuality]; exporter.outputURL=url; exporter.outputFileType = AVFileTypeQuickTimeMovie; exporter.shouldOptimizeForNetworkUse = YES; exporter.videoComposition = mainCompositionInst; [exporter exportAsynchronouslyWithCompletionHandler:^{ dispatch_async(dispatch_get_main_queue(), ^{ [self exportDidFinish:exporter]; }); }]; } </code></pre> <p>The problem is that the first time I use this function to export a portrait video, the variable <strong>videoTransform (videoAssetTrack.preferredTransform)</strong> are:</p> <pre><code>videoTransform.a == 0 && videoTransform.b == 1.0 && videoTransform.c == -1.0 && videoTransform.d == 0 </code></pre> <p>And the variable <strong>isVideoAssetPortrait_</strong> equals <strong>YES</strong>. Everything is right. However, after exporting completed and saved to Camera Roll, I used this function reload <strong>the result video</strong>. This time, the <strong>videoTransform</strong> changed:</p> <pre><code>videoTransform.a == 1.0 && videoTransform.b == 0 && videoTransform.c == 0 && videoTransform.d == 1.0 </code></pre> <p>And <strong>isVideoAssetPortrait_</strong> equals <strong>NO</strong>. It means that after one time export, the <strong>videoTransform</strong> has changed it's values (orientation from portrait -> landscape)</p> <p>I googled many questions about video orientation of AV Foundation, but there hasn't found the solution yet.</p> <p>Thank you for reading my long explanation. If you have any question, please let me know.</p>

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