Combine multiple videos in iOS using AVMutableVideoComposition

• AVMutableComposition object. It will be our tracks.
  AVMutableComposition

  AVMutableComposition *mixComposition = [[AVMutableComposition alloc] init]; 

• An array of instructions for the tracks and an AVMutableVideoCompositionInstruction object for them.
  AVMutableVideoCompositionInstruction

   NSMutableArray *arrayInstruction = [[NSMutableArray alloc] init]; AVMutableVideoCompositionInstruction *MainInstruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction]; 

• General audio track. The variable isSound indicates whether it is needed here (according to the task, the user could record video with or without sound).
  
  General audio track

    AVMutableCompositionTrack *audioTrack; if(self.isSoundOn==YES) audioTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid]; 

• Variable for storing the duration (and also it is needed to determine the bounding boundary).

    CMTime duration = kCMTimeZero; 

• Run through all the files and create assets for each of them. All this can and should be done in a loop, the variable i-here is the file index.
  
  Creating Assets

  All videos I recorded in the tempo directory, while increasing the value of i. Accordingly, assets are created from these files.

   AVAsset *currentAsset = [AVAsset assetWithURL:[NSURL fileURLWithPath:[NSString stringWithFormat:@"%@%@%d%@", NSTemporaryDirectory(), @"Movie",i,@".mov"]]]; 

• In the loop, AVMutableCompositionTrack is created, into each of which the time interval CMTimeRange from the created asset is inserted.
  Creating tracks

   //VIDEO TRACK AVMutableCompositionTrack *currentTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid]; [currentTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, currentAsset.duration) ofTrack:[[currentAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0] atTime:duration error:nil]; 

  Particular attention here should be paid to exactly where to insert the segment, if you want to avoid black bars during playback, or worse, overlaying one video over another during playback. And do not even ask why I focus on this attention.

• AVMutableVideoCompositionLayerInstruction is used to create instructions for a specific track layer. It is recorded in it possible transformation.
  AVMutableVideoCompositionLayerInstruction

   AVMutableVideoCompositionLayerInstruction *currentAssetLayerInstruction = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:currentTrack]; 

  If you correctly determine the position of the video (portrait or landscape) at the output, you can get a smart picture in which the horizontal or vertical video will be centered depending on the track in which mode you go first.

• The AVAssetTrack object is needed to create a track based on an existing asset with the AVMediaTypeVideo type.
  
  AVAssetTrack

   AVAssetTrack *currentAssetTrack = [[currentAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0]; 

• Increase the duration .
  
  duration UP

  CMTime even requires a separate post, of course.

   duration=CMTimeAdd(duration, currentAsset.duration); 

• timeRange

  The total duration of the video track.

   MainInstruction.timeRange = CMTimeRangeMake(kCMTimeZero, duration); 

• layerInstructions

  Here we need an array of instructions, formed in the second stage.

   MainInstruction.layerInstructions = arrayInstruction; 

• MainCompositionInst

  Create an instance of MainCompositionInst with the necessary parameters

    AVMutableVideoComposition *MainCompositionInst = [AVMutableVideoComposition videoComposition]; MainCompositionInst.instructions = [NSArray arrayWithObject:MainInstruction]; MainCompositionInst.frameDuration = CMTimeMake(1, 30); MainCompositionInst.renderSize = CGSizeMake(320.0, 480.0); 

• Where to save something?

   NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES); NSString *documentsDirectory = [paths objectAtIndex:0]; NSString *myPathDocs = [documentsDirectory stringByAppendingPathComponent:[NSString stringWithFormat:@"mergeVideo-%d.mov",arc4random() % 1000]]; NSURL *url = [NSURL fileURLWithPath:myPathDocs]; 

• We set quality and we create session

    NSString *quality = AVAssetExportPresetHighestQuality; if(self.isHighQuality==NO) quality = AVAssetExportPresetMediumQuality; AVAssetExportSession *exporter = [[AVAssetExportSession alloc] initWithAsset:mixComposition presetName:quality]; 

• Save!

   exporter.outputURL=url; exporter.outputFileType = AVFileTypeQuickTimeMovie; exporter.videoComposition = MainCompositionInst; exporter.shouldOptimizeForNetworkUse = YES; [exporter exportAsynchronouslyWithCompletionHandler:^ { //    . }]; 

  switch (exporter.status) { case AVAssetExportSessionStatusCompleted: NSLog(@"Completed exporting!"); break; case AVAssetExportSessionStatusFailed: NSLog(@"Failed:%@", exporter.error.description); break; case AVAssetExportSessionStatusCancelled: NSLog(@"Canceled:%@", exporter.error); break; case AVAssetExportSessionStatusExporting: NSLog(@"Exporting!"); break; case AVAssetExportSessionStatusWaiting: NSLog(@"Waiting"); break; default: break; } 

Conclusion