How to do Slow Motion video in IOS

You could scale video using AVFoundation and CoreMedia frameworks.Take a look at the AVMutableCompositionTrack method:

- (void)scaleTimeRange:(CMTimeRange)timeRange toDuration:(CMTime)duration;

Sample:

AVURLAsset* videoAsset = nil; //self.inputAsset;//create mutable compositionAVMutableComposition *mixComposition = [AVMutableComposition composition];AVMutableCompositionTrack *compositionVideoTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeVideo                                                                               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;}//slow down whole video by 2.0double videoScaleFactor = 2.0;CMTime videoDuration = videoAsset.duration;[compositionVideoTrack scaleTimeRange:CMTimeRangeMake(kCMTimeZero, videoDuration)                           toDuration:CMTimeMake(videoDuration.value*videoScaleFactor, videoDuration.timescale)];//exportAVAssetExportSession* assetExport = [[AVAssetExportSession alloc] initWithAsset:mixComposition                                                                     presetName:AVAssetExportPresetLowQuality];

(Probably audio track from videoAsset should also be added to mixComposition)

Slower + Faster with or without audio track

I have tried and able to Slower the asset.

compositionVideoTrack?.scaleTimeRange(timeRange, toDuration: scaledVideoDuration) did the trick.

I made a class which will help you to generate a slower video from AVAsset. + point is you can also make it faster and another + point is it will handle the audio too.

Here is my custom class sample:

import UIKitimport AVFoundationenum SpeedoMode {    case Slower    case Faster}class VSVideoSpeeder: NSObject {    /// Singleton instance of `VSVideoSpeeder`    static var shared: VSVideoSpeeder = {       return VSVideoSpeeder()    }()    /// Range is b/w 1x, 2x and 3x. Will not happen anything if scale is out of range. Exporter will be nil in case url is invalid or unable to make asset instance.    func scaleAsset(fromURL url: URL,  by scale: Int64, withMode mode: SpeedoMode, completion: @escaping (_ exporter: AVAssetExportSession?) -> Void) {        /// Check the valid scale        if scale < 1 || scale > 3 {            /// Can not proceed, Invalid range            completion(nil)            return        }        /// Asset        let asset = AVAsset(url: url)        /// Video Tracks        let videoTracks = asset.tracks(withMediaType: AVMediaType.video)        if videoTracks.count == 0 {            /// Can not find any video track            completion(nil)            return        }        /// Get the scaled video duration        let scaledVideoDuration = (mode == .Faster) ? CMTimeMake(asset.duration.value / scale, asset.duration.timescale) : CMTimeMake(asset.duration.value * scale, asset.duration.timescale)        let timeRange = CMTimeRangeMake(kCMTimeZero, asset.duration)        /// Video track        let videoTrack = videoTracks.first!        let mixComposition = AVMutableComposition()        let compositionVideoTrack = mixComposition.addMutableTrack(withMediaType: AVMediaType.video, preferredTrackID: kCMPersistentTrackID_Invalid)        /// Audio Tracks        let audioTracks = asset.tracks(withMediaType: AVMediaType.audio)        if audioTracks.count > 0 {            /// Use audio if video contains the audio track            let compositionAudioTrack = mixComposition.addMutableTrack(withMediaType: AVMediaType.audio, preferredTrackID: kCMPersistentTrackID_Invalid)            /// Audio track            let audioTrack = audioTracks.first!            do {                try compositionAudioTrack?.insertTimeRange(timeRange, of: audioTrack, at: kCMTimeZero)                compositionAudioTrack?.scaleTimeRange(timeRange, toDuration: scaledVideoDuration)            } catch _ {                /// Ignore audio error            }        }        do {            try compositionVideoTrack?.insertTimeRange(timeRange, of: videoTrack, at: kCMTimeZero)            compositionVideoTrack?.scaleTimeRange(timeRange, toDuration: scaledVideoDuration)            /// Keep original transformation            compositionVideoTrack?.preferredTransform = videoTrack.preferredTransform            /// Initialize Exporter now            let outputFileURL = URL(fileURLWithPath: "/Users/thetiger/Desktop/scaledVideo.mov")           /// Note:- Please use directory path if you are testing with device.            if FileManager.default.fileExists(atPath: outputFileURL.absoluteString) {                try FileManager.default.removeItem(at: outputFileURL)            }            let exporter = AVAssetExportSession(asset: mixComposition, presetName: AVAssetExportPresetHighestQuality)            exporter?.outputURL = outputFileURL            exporter?.outputFileType = AVFileType.mov            exporter?.shouldOptimizeForNetworkUse = true            exporter?.exportAsynchronously(completionHandler: {                completion(exporter)            })        } catch let error {            print(error.localizedDescription)            completion(nil)            return        }    }}

I took 1x, 2x and 3x as a valid scale. Class contains the proper validation and handling. Below is the sample of how to use this function.

let url = Bundle.main.url(forResource: "1", withExtension: "mp4")!VSVideoSpeeder.shared.scaleAsset(fromURL: url, by: 3, withMode: SpeedoMode.Slower) { (exporter) in     if let exporter = exporter {         switch exporter.status {                case .failed: do {                      print(exporter.error?.localizedDescription ?? "Error in exporting..")                }                case .completed: do {                      print("Scaled video has been generated successfully!")                }                case .unknown: break                case .waiting: break                case .exporting: break                case .cancelled: break           }      }      else {           /// Error           print("Exporter is not initialized.")      }}

This line will handle the audio scaling

compositionAudioTrack?.scaleTimeRange(timeRange, toDuration: scaledVideoDuration)

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 compositionAVMutableComposition *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 2.0double 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];//exportAVAssetExportSession* 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.");}}