iOS AVFoundation - Converting video into images at 60 fps

Question

i'm trying to convert a whole video into a sequence of images at a rate of 60fps, which means 60 images generated per second of video...

To do so, i'm making use of AVAssetImageGenerator and the generateCGImagesAsynchronouslyForTimes method ...

Things go quite well except that i'm having serious performance issues regarging the batch processing execution time (approximately 5 mins for 13 seconds video) ...

Moreover, above the following size CGSizeMake(512, 324), i experience crashes ...

Did anyone already have experience with this kind of processing and knows how to reduce this time execution as well as being able to extract the images at a higher resolution ?

Below is the code i'm testing ...

NSURL *movieURL = [NSURL fileURLWithPath:getCaptureMoviePath()];

AVURLAsset *asset=[[AVURLAsset alloc] initWithURL:movieURL options:nil];
AVAssetImageGenerator *generator = [[AVAssetImageGenerator alloc]  initWithAsset:asset];
generator.appliesPreferredTrackTransform=TRUE;
generator.requestedTimeToleranceAfter=kCMTimeZero;
generator.requestedTimeToleranceBefore=kCMTimeZero;
NSMutableArray *thumbTimes=[NSMutableArray arrayWithCapacity:asset.duration.value];

for(int t=0;t < asset.duration.value;t=t+2) {
    CMTime thumbTime = CMTimeMake(t, asset.duration.timescale);
    NSLog(@"Time Scale : %d ", asset.duration.timescale);
    NSValue *v=[NSValue valueWithCMTime:thumbTime];
        [thumbTimes addObject:v];
}
NSLog(@"thumbTimes array contains %d objects : ", [thumbTimes count]);
[asset release];
AVAssetImageGeneratorCompletionHandler handler = ^(CMTime requestedTime, CGImageRef im, CMTime actualTime, AVAssetImageGeneratorResult result, NSError *error) {
    if (result != AVAssetImageGeneratorSucceeded) {
        NSLog(@"couldn't generate thumbnail, error:%@", error);
    } else {
        NSLog(@"actual time: %lld/%d (requested: %lld/%d)",actualTime.value,actualTime.timescale,requestedTime.value,requestedTime.timescale);
        NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
        [formatter setDateFormat:@"yyyyMMdd-HHmmss"];
        NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
        NSString *documentsDirectory = [paths objectAtIndex:0];
        NSString *filename = [NSString stringWithFormat:@"%@.png", [formatter stringFromDate:[NSDate date]]];
        NSString *filepath = [documentsDirectory stringByAppendingPathComponent:filename];
        CFURLRef url = (CFURLRef)[NSURL fileURLWithPath:filepath];
        CGImageDestinationRef destination = CGImageDestinationCreateWithURL(url, kUTTypePNG, 1, NULL);
        CGImageDestinationAddImage(destination, im, nil);
        if (!CGImageDestinationFinalize(destination)) {     
            NSLog(@"Failed to write image to %@", filepath);
        }
        CFRelease(destination);
    }
    //[generator release];
};
CGSize maxSize = CGSizeMake(512, 324);
generator.maximumSize = maxSize;

[generator generateCGImagesAsynchronouslyForTimes:thumbTimes completionHandler:handler];

Thanking you in advance,

j.

Answer 1

Hey @Sooriah Joel try using following code. It is working fine for me.

- (void)generateCMTimesArrayOfAllFramesUsingAsset:(AVURLAsset *)asset
{
    if (cmTimeArray.count>0) {
        [cmTimeArray removeAllObjects];
    }
    //Generate all frames present in video
    for(int t=0;t < asset.duration.value;t++) {
        CMTime thumbTime = CMTimeMake(t,asset.duration.timescale);
        NSValue *v=[NSValue valueWithCMTime:thumbTime];
        [cmTimeArray addObject:v];
    }
    NSLog(@"Array of time %@ count = %d",cmTimeArray, cmTimeArray.count);
    //NSLog(@"Array count = %d",cmTimeArray.count);
}


- (void)generateCMTimesArrayOfFrames:(int)framesInterval UsingAsset:(AVURLAsset *)asset
{
    int videoDuration = ceilf(((float)asset.duration.value/asset.duration.timescale));
    NSLog(@"Video duration %lld seconds timescale = %d",asset.duration.value,asset.duration.timescale);
    if (cmTimeArray.count>0) {
        [cmTimeArray removeAllObjects];
    }
    //Generate limited frames present in video
    for (int i = 0; i<videoDuration; i++)
   {
       int64_t tempInt = i;
       CMTime tempCMTime = CMTimeMake(tempInt,1);
       int32_t interval = framesInterval;
       for (int j = 1; j<framesInterval+1; j++)
       {
            CMTime newCMtime = CMTimeMake(j,interval);
            CMTime addition = CMTimeAdd(tempCMTime, newCMtime);
            [cmTimeArray addObject:[NSValue valueWithCMTime:addition]];
       }
   }
   NSLog(@"Array of time %@ count = %d",cmTimeArray, cmTimeArray.count);
   //NSLog(@"Array count = %d",cmTimeArray.count);
}


- (void)generateThumbnailsFromVideoURL:(AVURLAsset *)videoAsset
{
    //Generate CMTimes Array of required frames
    //1.Generate All Frames
    //[self generateCMTimesArrayOfAllFramesUsingAsset:asset];

    //2.Generate specific frames per second
    [self generateCMTimesArrayOfFrames:30 UsingAsset:videoAsset];

    __block int i = 0;
    AVAssetImageGeneratorCompletionHandler handler = ^(CMTime requestedTime, CGImageRef im, CMTime actualTime, AVAssetImageGeneratorResult result, NSError *error){
    if (result == AVAssetImageGeneratorSucceeded) {
        [framesArray addObject:[UIImage imageWithCGImage:im]];
    }
    if (result == AVAssetImageGeneratorFailed) {
        NSLog(@"Failed with error: %@ code %d", [error localizedDescription],error.code);
    }
    if (result == AVAssetImageGeneratorCancelled) {
        NSLog(@"Canceled");
    }

    i++;
    imageIndex = i;

    if(i == cmTimeArray.count) {
        //Thumbnail generation completed
    }
};

    // Launching the process...
    self.generator = [[AVAssetImageGenerator alloc] initWithAsset:videoAsset];
    self.generator.apertureMode = AVAssetImageGeneratorApertureModeCleanAperture;
    self.generator.appliesPreferredTrackTransform=TRUE;
    self.generator.requestedTimeToleranceBefore = kCMTimeZero;
    self.generator.requestedTimeToleranceAfter = kCMTimeZero;
    self.generator.maximumSize = CGSizeMake(40, 40);
    [self.generator generateCGImagesAsynchronouslyForTimes:cmTimeArray completionHandler:handler];
}