Mini Tutorial: How to capture video of iPhone app in Cocos2D? with audio

Okay, so I figured out how to add audio to my video.

In my previous blog post (, I managed to take a video of my app and save it into a file. However I am just stringing together screenshots of my app taken at every 0.1 second, so it doesn’t capture the audio.

So I have a different function that is capturing my audio (AVAudioRecorder), and saving that into a file.

Now, to combine the files together. Since iOS 4.1, AVFoundation included this thing called AVMutableComposition, and with that you can make composites of stuff, like combine video and audio files together to make a new video file that has audio.

So code bits (I found bits of the code in StackOverflow):

-(void) processVideo: (NSURL*) videoUrl
    AVURLAsset* videoAsset = [[AVURLAsset alloc]initWithURL: videoUrl options:nil];
    AVMutableComposition* mixComposition = [AVMutableComposition composition];
    AppDelegate *appDelegate = (AppDelegate *)[[UIApplication sharedApplication] delegate];
    NSError * error = nil;
    for (NSMutableDictionary * audioInfo in appDelegate.audioInfoArray)
        NSString *pathString = [[NSHomeDirectory() stringByAppendingString:@”/Documents/”] stringByAppendingString: [audioInfo objectForKey: @”fileName”]];
        AVURLAsset * urlAsset = [AVURLAsset URLAssetWithURL:[NSURL fileURLWithPath:pathString] options:nil];
        AVAssetTrack * audioAssetTrack = [[urlAsset tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0];
        AVMutableCompositionTrack *compositionAudioTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeAudio
                                                                                       preferredTrackID: kCMPersistentTrackID_Invalid];
        NSLog(@”%lf”, [[audioInfo objectForKey: @”startTime”] doubleValue]);
        CMTime audioStartTime = CMTimeMake(([[audioInfo objectForKey: @”startTime”] doubleValue]*TIME_SCALE), TIME_SCALE);
        [compositionAudioTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero,urlAsset.duration) ofTrack:audioAssetTrack atTime:audioStartTime error:&error];     
    AVMutableCompositionTrack *compositionVideoTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeVideo
    [compositionVideoTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, videoAsset.duration)
                                   ofTrack:[[videoAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0]
                                    atTime:kCMTimeZero error:nil];
    AVAssetExportSession* _assetExport = [[AVAssetExportSession alloc] initWithAsset:mixComposition
    NSString* videoName = @””;
    NSString *exportPath = [[self pathToDocumentsDirectory] stringByAppendingPathComponent:videoName];
    NSURL    *exportUrl = [NSURL fileURLWithPath:exportPath];
    if ([[NSFileManager defaultManager] fileExistsAtPath:exportPath])
        [[NSFileManager defaultManager] removeItemAtPath:exportPath error:nil];
    _assetExport.outputFileType = @””;
    NSLog(@”file type %@”,_assetExport.outputFileType);
    _assetExport.outputURL = exportUrl;
    _assetExport.shouldOptimizeForNetworkUse = YES;
    [_assetExport exportAsynchronouslyWithCompletionHandler:
     ^(void ) {
         switch (_assetExport.status)
             case AVAssetExportSessionStatusCompleted:
                 //export complete
                 NSLog(@”Export Complete”);
                 //[self uploadToYouTube];
             case AVAssetExportSessionStatusFailed:
                 NSLog(@”Export Failed”);
                 NSLog(@”ExportSessionError: %@”, [_assetExport.error localizedDescription]);
                 //export error (see exportSession.error) 
             case AVAssetExportSessionStatusCancelled:
                 NSLog(@”Export Failed”);
                 NSLog(@”ExportSessionError: %@”, [_assetExport.error localizedDescription]);
                 //export cancelled 

I have more than one audio file that I want to combine with my video, so I created a array file that contains information for each of the audio files (such as where the file is located and when to play that audio).

And that’s it 🙂 You have a video of your app 🙂 with audio 🙂


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