Can't have AVAssetImageGenerator give me all the frames of a movie

问题

I can't have AVAssetImageGenerator give me all the frames of a movie.

Using this code:

NSString *path = [[NSBundle mainBundle] pathForResource:@"video" ofType:@"mov"];
NSURL *url=[NSURL fileURLWithPath:path];
NSDictionary *options = [NSDictionary dictionaryWithObject:[NSNumber numberWithBool:YES] forKey:AVURLAssetPreferPreciseDurationAndTimingKey];
self.asset=[[AVURLAsset alloc] initWithURL:url options:options];

NSMutableArray *thumbTimes=[NSMutableArray arrayWithCapacity:asset.duration.value];
for(int t=0;t < asset.duration.value;t++) {
    CMTime thumbTime = CMTimeMake(t,asset.duration.timescale);
    NSValue *v=[NSValue valueWithCMTime:thumbTime];
    [thumbTimes addObject:v];
}
self.generator = [[AVAssetImageGenerator alloc] initWithAsset:asset];
self.generator.appliesPreferredTrackTransform=TRUE;
self.generator.requestedTimeToleranceAfter=kCMTimeZero;
self.generator.requestedTimeToleranceBefore=kCMTimeZero;


AVAssetImageGeneratorCompletionHandler handler = ^(CMTime requestedTime, CGImageRef im, CMTime actualTime, AVAssetImageGeneratorResult result, NSError *error){
    if (result != AVAssetImageGeneratorSucceeded) {
        NSLog(@"couldn't generate thumbnail, error:%@", error);
    }
    NSLog(@"actual time: %lld/%d (requested: %lld/%d)",actualTime.value,actualTime.timescale,requestedTime.value,requestedTime.timescale);
};
CGSize maxSize = CGSizeMake(320, 180);
generator.maximumSize = maxSize;
[generator generateCGImagesAsynchronouslyForTimes:thumbTimes completionHandler:handler];

I get:

2012-04-19 18:55:06.801 OpenCVClient[77273:13b07] actual time: -9/600 (requested: 0/600)
2012-04-19 18:55:07.836 OpenCVClient[77273:13b07] actual time: -9/600 (requested: 1/600)
2012-04-19 18:55:08.314 OpenCVClient[77273:13b07] actual time: -9/600 (requested: 2/600)
2012-04-19 18:55:09.350 OpenCVClient[77273:13b07] actual time: -9/600 (requested: 3/600)
2012-04-19 18:55:10.186 OpenCVClient[77273:13b07] actual time: -9/600 (requested: 4/600)
2012-04-19 18:55:11.257 OpenCVClient[77273:13b07] actual time: -9/600 (requested: 5/600)
2012-04-19 18:55:11.697 OpenCVClient[77273:13b07] actual time: -9/600 (requested: 6/600)
2012-04-19 18:55:12.246 OpenCVClient[77273:13b07] actual time: -9/600 (requested: 7/600)
2012-04-19 18:55:13.255 OpenCVClient[77273:13b07] actual time: -9/600 (requested: 8/600)
2012-04-19 18:55:14.513 OpenCVClient[77273:13b07] actual time: -9/600 (requested: 9/600)
2012-04-19 18:55:15.944 OpenCVClient[77273:13b07] actual time: -9/600 (requested: 10/600)
2012-04-19 18:55:17.230 OpenCVClient[77273:13b07] actual time: 11/600 (requested: 11/600)
2012-04-19 18:55:17.995 OpenCVClient[77273:13b07] actual time: 11/600 (requested: 12/600)
2012-04-19 18:55:18.716 OpenCVClient[77273:13b07] actual time: 11/600 (requested: 13/600)
2012-04-19 18:55:19.399 OpenCVClient[77273:13b07] actual time: 11/600 (requested: 14/600)

As you can see in the code I've tried to set AVURLAssetPreferPreciseDurationAndTimingKey, requestedTimeToleranceBefore and requestedTimeToleranceAfter with no effect.

Any ideas?

回答1:

With your code you get all frame of movie. Difference between requested and actual time is caused by movie framerate. It seems, your movie has approx. 25-29 fps. So for example there isn't difference frame between time 1/600s and 8/600s.

回答2:

    //loading image
    NSString *initialURL = [NSString stringWithFormat:@"%@",[arrayURL objectAtIndex:indexPath.row]];
    NSURL *url=[NSURL fileURLWithPath:initialURL];
    NSDictionary *options = [NSDictionary dictionaryWithObject:[NSNumber numberWithBool:YES] forKey:AVURLAssetPreferPreciseDurationAndTimingKey];
    self.asset=[[AVURLAsset alloc] initWithURL:url options:options];

    NSMutableArray *thumbTimes=[NSMutableArray arrayWithCapacity:asset.duration.value];
    CMTime thumbTime = CMTimeMake(1,1);
    NSValue *v=[NSValue valueWithCMTime:thumbTime];
    [thumbTimes addObject:v];

    self.imageGenerator = [[AVAssetImageGenerator alloc] initWithAsset:asset];
    self.imageGenerator.appliesPreferredTrackTransform=TRUE;
    self.imageGenerator.requestedTimeToleranceAfter=kCMTimeZero;
    self.imageGenerator.requestedTimeToleranceBefore=kCMTimeZero;


    AVAssetImageGeneratorCompletionHandler handler = ^(CMTime requestedTime, CGImageRef im, CMTime actualTime, AVAssetImageGeneratorResult result, NSError *error){
        if (result != AVAssetImageGeneratorSucceeded) {
            NSLog(@"couldn't generate thumbnail, error:%@", error);
        }
        NSLog(@"actual time: %lld/%d (requested: %lld/%d)",actualTime.value,actualTime.timescale,requestedTime.value,requestedTime.timescale);

        //your image view
        imageView.image = [UIImage imageWithCGImage:im];
    };
    CGSize maxSize = CGSizeMake(320, 180);
    imageGenerator.maximumSize = maxSize;
    [imageGenerator generateCGImagesAsynchronouslyForTimes:thumbTimes completionHandler:handler];
    //loaging complete

来源：https://stackoverflow.com/questions/10232072/cant-have-avassetimagegenerator-give-me-all-the-frames-of-a-movie