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.

Ref: http://www.youtube.com/watch?v=BJ3_xMGzauk (watch from 0 to 10s)

From my analysis, I've found that AVFoundation framework can be helpful.

Ref: http://developer.apple.com/library/ios/#documentation/AudioVideo/Conceptual/AVFoundationPG/Articles/00_Introduction.html

Copy and pasted from the above link:

" Editing AV Foundation uses compositions to create new assets from existing pieces of media (typically, one or more video and audio tracks). You use a mutable composition to add and remove tracks, and adjust their temporal orderings. You can also set the relative volumes and ramping of audio tracks; and set the opacity, and opacity ramps, of video tracks. A composition is an assemblage of pieces of media held in memory. When you export a composition using an export session, it's collapsed to a file. On iOS 4.1 and later, you can also create an asset from media such as sample buffers or still images using an asset writer.

"

Questions: Can I do " slow motion " the video/audio file using the AVFoundation framework ? Or Is there any other package available? If i want to handle audio and video separately, please guide me how to do?

Update :: Code For AV Export Session :

 NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);     NSString *outputURL = paths[0];     NSFileManager *manager = [NSFileManager defaultManager];     [manager createDirectoryAtPath:outputURL withIntermediateDirectories:YES attributes:nil error:nil];     outputURL = [outputURL stringByAppendingPathComponent:@"output.mp4"];     // Remove Existing File     [manager removeItemAtPath:outputURL error:nil];     AVAssetExportSession *exportSession = [[AVAssetExportSession alloc] initWithAsset:self.inputAsset presetName:AVAssetExportPresetLowQuality];     exportSession.outputURL = [NSURL fileURLWithPath:outputURL]; // output path;     exportSession.outputFileType = AVFileTypeQuickTimeMovie;     [exportSession exportAsynchronouslyWithCompletionHandler:^(void) {         if (exportSession.status == AVAssetExportSessionStatusCompleted) {             [self writeVideoToPhotoLibrary:[NSURL fileURLWithPath:outputURL]];             ALAssetsLibrary *library = [[ALAssetsLibrary alloc] init];             [library writeVideoAtPathToSavedPhotosAlbum:[NSURL fileURLWithPath:outputURL] completionBlock:^(NSURL *assetURL, NSError *error){                 if (error) {                     NSLog(@"Video could not be saved");                 }             }];         } else {             NSLog(@"error: %@", [exportSession error]);         }     }]; 

Answer 1

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 composition AVMutableComposition *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 2.0 double videoScaleFactor = 2.0; CMTime videoDuration = videoAsset.duration;  [compositionVideoTrack scaleTimeRange:CMTimeRangeMake(kCMTimeZero, videoDuration)                            toDuration:CMTimeMake(videoDuration.value*videoScaleFactor, videoDuration.timescale)];  //export AVAssetExportSession* assetExport = [[AVAssetExportSession alloc] initWithAsset:mixComposition                                                                      presetName:AVAssetExportPresetLowQuality]; 

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

Answer 2

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 UIKit import AVFoundation  enum 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)