Question

每当我尝试从我的视频资源生成静止帧时，它就会在0.000 ..秒时生成。我可以从我的日志消息中看到这一点。好消息是我可以在0.000 ..时获得图像，以显示在名为“myImageView”的UIImageView中。我认为问题是没有设置AVURLAssetPreferPreciseDurationAndTimingKey，但即使在我弄清楚如何做到这一点之后，它仍然无法正常运行..

这是我的......

time，actualTime和generate在Header中声明

NSString *path = [NSHomeDirectory() stringByAppendingPathComponent:[NSString stringWithFormat:@"Documents/videoTest4.m4v"]];
//UISaveVideoAtPathToSavedPhotosAlbum(path, self, @selector(video:didFinishSavingWithError:contextInfo:), nil);
NSURL *url = [NSURL fileURLWithPath:path];

NSDictionary *options = [NSDictionary dictionaryWithObject:[NSNumber numberWithBool:YES] forKey:AVURLAssetPreferPreciseDurationAndTimingKey];
AVURLAsset *asset = [[AVURLAsset alloc] initWithURL:url options:options];

Float64 durationSeconds = CMTimeGetSeconds([asset duration]);

generate = [[AVAssetImageGenerator alloc] initWithAsset:asset];
NSError *err = nil;

time = CMTimeMake(600,600.0);
CGImageRef imgRef = [generate copyCGImageAtTime:time actualTime:&actualTime error:&err];
UIImage *currentImg = [[UIImage alloc] initWithCGImage:imgRef];
myImageView.image = currentImg;

NSLog(@"The total Video Duration is %f",durationSeconds);
NSLog(@"The time I want my image is %f",CMTimeGetSeconds(time));
NSLog(@"The actual time my image was take was %f",CMTimeGetSeconds(actualTime));

我的控制台读取..

2011-04-28 18：49：59.062 videoTest [26553：207]总视频时长为1.880000

2011-04-28 18：49：59.064 videoTest [26553：207]我想要的图片时间是1.000000

2011-04-28 18：49：59.064 videoTest [26553：207]我的拍摄时间实际为0.000000

..........................

提前多谢你们..：）

Answer 1

要解决此问题，您只需将 requestedTimeToleranceBefore 和 requestedTimeToleranceAfter 设置为kCMTimeZero for AVAssetImageGenerator。

AVAssetImageGenerator Class Reference

Answer 2

昨晚深夜，我有一个想法，确定今天早上有效。基本上我只是创建一个新的合成资产，然后创建一个时间范围，表示视频的一帧，每秒24帧。一旦我创建了这些组合，我就抓住每个组合的第一帧。我为每个帧执行此操作并创建一个包含所有帧的数组。这就是我做的..

NSString *path = [NSHomeDirectory() stringByAppendingPathComponent:[NSString stringWithFormat:@"Documents/videoTest4.m4v"]];
//UISaveVideoAtPathToSavedPhotosAlbum(path, self, @selector(video:didFinishSavingWithError:contextInfo:), nil);
NSURL *url = [NSURL fileURLWithPath:path];

NSDictionary *options = [NSDictionary dictionaryWithObject:[NSNumber numberWithBool:YES] forKey:AVURLAssetPreferPreciseDurationAndTimingKey];
AVURLAsset *asset = [[AVURLAsset alloc] initWithURL:url options:options];

Float64 durationFrames = CMTimeGetSeconds([asset duration]) * 24.0;

AVMutableComposition *myComp = [AVMutableComposition composition];

AVMutableCompositionTrack *compositionVideoTrack = [myComp addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];

NSError *error = nil;
BOOL ok = NO;

NSMutableArray* frameArray = [[NSMutableArray alloc] init];

generate = [[AVAssetImageGenerator alloc] initWithAsset:myComp];
NSError *err = nil;

for (int i = 0; i < floor(durationFrames); i++) {

    CMTime startTime = CMTimeMake(i, 24);
    CMTime endTime = CMTimeMake(i+1, 24);

    CMTimeRange myRange = CMTimeRangeMake(startTime, endTime);

    AVAssetTrack *sourceVideoTrack = [[asset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0];
    ok = [compositionVideoTrack insertTimeRange:myRange ofTrack:sourceVideoTrack atTime:kCMTimeZero error:&error];
    if (!ok) {
        // Deal with the error.
    }

    time = CMTimeMake(0,1);
    CGImageRef imgRef = [generate copyCGImageAtTime:time actualTime:&actualTime error:&err];
    UIImage *currentImg = [[UIImage alloc] initWithCGImage:imgRef];
    [frameArray addObject:currentImg];

    [currentImg release];

}

NSLog(@"This video is calculated at %f Frames..",durationFrames);
NSLog(@"You made a total of %i Frames!!",[frameArray count]);

然后控制台读取..

2011-04-29 10：42：24.292 videoTest [29019：207]此视频以45.120000帧计算..

2011-04-29 10：42：24.293 videoTest [29019：207]你共制作了45帧!!

我无法从1.8秒的视频中获得精确的CMTime来生成静止图像

2 个答案: