iphone - 不能让 AVAssetImageGenerator 给我电影的所有帧

Question

我不能让 AVAssetImageGenerator 给我电影的所有帧。

使用这段代码:

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];

我得到:

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)

正如您在代码中看到的那样，我尝试设置 AVURLAssetPreferPreciseDurationAndTimingKey、requestedTimeToleranceBefore 和 requestedTimeToleranceAfter 但没有任何效果。

有什么想法吗？

Answer 1

使用您的代码，您可以获得电影的所有帧。请求时间和实际时间之间的差异是由电影帧率引起的。看来，你的电影有大约。 25-29 帧/秒。因此，例如时间 1/600s 和 8/600s 之间没有差异帧。