How to do Slow Motion video in IOS

Question

I have to do \"slow motion\" in a video file along with audio, in-between some frames and need to store the ramped video as a new video.

Answer 1

I have achieved on adding slow motion to video including audio as well with proper output orientation.

 - (void)SlowMotion:(NSURL *)URl
 {
   AVURLAsset* videoAsset = [AVURLAsset URLAssetWithURL:URl options:nil]; //self.inputAsset;

AVAsset *currentAsset = [AVAsset assetWithURL:URl];
AVAssetTrack *vdoTrack = [[currentAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0];
//create mutable composition
AVMutableComposition *mixComposition = [AVMutableComposition composition];

AVMutableCompositionTrack *compositionVideoTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];
AVMutableCompositionTrack *compositionAudioTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];

NSError *videoInsertError = nil;
BOOL videoInsertResult = [compositionVideoTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, videoAsset.duration)
                                                        ofTrack:[[videoAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0]
                                                         atTime:kCMTimeZero
                                                          error:&videoInsertError];
if (!videoInsertResult || nil != videoInsertError) {
    //handle error
    return;
}

NSError *audioInsertError =nil;
BOOL audioInsertResult =[compositionAudioTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, videoAsset.duration)
                                                       ofTrack:[[currentAsset tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0]
                                                        atTime:kCMTimeZero
                                                         error:&audioInsertError];

if (!audioInsertResult || nil != audioInsertError) {
    //handle error
    return;
}

CMTime duration =kCMTimeZero;
duration=CMTimeAdd(duration, currentAsset.duration);
//slow down whole video by 2.0
double videoScaleFactor = 2.0;
CMTime videoDuration = videoAsset.duration;

[compositionVideoTrack scaleTimeRange:CMTimeRangeMake(kCMTimeZero, videoDuration)
                           toDuration:CMTimeMake(videoDuration.value*videoScaleFactor, videoDuration.timescale)];
[compositionAudioTrack scaleTimeRange:CMTimeRangeMake(kCMTimeZero, videoDuration)
                           toDuration:CMTimeMake(videoDuration.value*videoScaleFactor, videoDuration.timescale)];
[compositionVideoTrack setPreferredTransform:vdoTrack.preferredTransform];

        NSArray *dirPaths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
        NSString *docsDir = [dirPaths objectAtIndex:0];
        NSString *outputFilePath = [docsDir stringByAppendingPathComponent:[NSString stringWithFormat:@"slowMotion.mov"]];
        if ([[NSFileManager defaultManager] fileExistsAtPath:outputFilePath])
        [[NSFileManager defaultManager] removeItemAtPath:outputFilePath error:nil];
        NSURL *_filePath = [NSURL fileURLWithPath:outputFilePath];

//export
AVAssetExportSession* assetExport = [[AVAssetExportSession alloc] initWithAsset:mixComposition
                                                                        presetName:AVAssetExportPresetLowQuality];
assetExport.outputURL=_filePath;
                          assetExport.outputFileType =           AVFileTypeQuickTimeMovie;
  exporter.shouldOptimizeForNetworkUse = YES;
                           [assetExport exportAsynchronouslyWithCompletionHandler:^
                            {

                                switch ([assetExport status]) {
                                    case AVAssetExportSessionStatusFailed:
                                    {
                                        NSLog(@"Export session faiied with error: %@", [assetExport error]);
                                        dispatch_async(dispatch_get_main_queue(), ^{
                                            // completion(nil);
                                        });
                                    }
                                        break;
                                    case AVAssetExportSessionStatusCompleted:
                                    {

                                        NSLog(@"Successful");
                                        NSURL *outputURL = assetExport.outputURL;

                                        ALAssetsLibrary *library = [[ALAssetsLibrary alloc] init];
                                        if ([library videoAtPathIsCompatibleWithSavedPhotosAlbum:outputURL]) {

                                            [self writeExportedVideoToAssetsLibrary:outputURL];
                                        }
                                        dispatch_async(dispatch_get_main_queue(), ^{
                                            //                                            completion(_filePath);
                                        });

                                    }
                                        break;
                                    default:

                                        break;
                                }


                            }];


 }

  - (void)writeExportedVideoToAssetsLibrary :(NSURL *)url {
NSURL *exportURL = url;
ALAssetsLibrary *library = [[ALAssetsLibrary alloc] init];
if ([library videoAtPathIsCompatibleWithSavedPhotosAlbum:exportURL]) {
    [library writeVideoAtPathToSavedPhotosAlbum:exportURL completionBlock:^(NSURL *assetURL, NSError *error){
        dispatch_async(dispatch_get_main_queue(), ^{
            if (error) {
                UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:[error localizedDescription]
                                                                    message:[error localizedRecoverySuggestion]
                                                                   delegate:nil
                                                          cancelButtonTitle:@"OK"
                                                          otherButtonTitles:nil];
                [alertView show];
            }
            if(!error)
            {
               // [activityView setHidden:YES];
                UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:@"Sucess"
                                                                    message:@"video added to gallery successfully"
                                                                   delegate:nil
                                                          cancelButtonTitle:@"OK"
                                                          otherButtonTitles:nil];
                [alertView show];
            }
 #if !TARGET_IPHONE_SIMULATOR
            [[NSFileManager defaultManager] removeItemAtURL:exportURL error:nil];
#endif
        });
    }];
} else {
    NSLog(@"Video could not be exported to assets library.");
}

}