iphone ios取出視頻的每一幀圖片（關鍵幀，AVAssetImageGenerator）

[mImageGenerator generateCGImagesAsynchronouslyForTimes:[NSArray arrayWithObject:[NSValue valueWithCMTime:CMTimeMakeWithSeconds(time, NSEC_PER_SEC)]] completionHandler:
    ^(CMTime requestedTime, CGImageRef image, CMTime actualTime, AVAssetImageGeneratorResult result, NSError *error)
    {

        NSLog(@"actual got image at time:%f", CMTimeGetSeconds(actualTime));
        if (image)
        {
            [CATransaction begin];
            [CATransaction setDisableActions:YES];
            [layer setContents:(id)image];

            //UIImage *img = [UIImage imageWithCGImage:image];
            //UIImageWriteToSavedPhotosAlbum(img, self, nil, nil);

            [CATransaction commit];
        }
    }];

如何取得第一幀

AVFoundationframework 

 CoreMediaframework

+ (UIImage*) thumbnailImageForVideo:(NSURL *)videoURL atTime:(NSTimeInterval)time {
    AVURLAsset *asset = [[[AVURLAsset alloc] initWithURL:videoURL options:nil] autorelease];
    NSParameterAssert(asset);
    AVAssetImageGenerator *assetImageGenerator = [[[AVAssetImageGenerator alloc] initWithAsset:asset] autorelease];
    assetImageGenerator.appliesPreferredTrackTransform = YES;
    assetImageGenerator.apertureMode = AVAssetImageGeneratorApertureModeEncodedPixels;

    CGImageRef thumbnailImageRef = NULL;
    CFTimeInterval thumbnailImageTime = time;
    NSError *thumbnailImageGenerationError = nil;
    thumbnailImageRef = [assetImageGenerator copyCGImageAtTime:CMTimeMake(thumbnailImageTime, 60) actualTime:NULL error:&thumbnailImageGenerationError];

    if (!thumbnailImageRef)
        NSLog(@"thumbnailImageGenerationError %@", thumbnailImageGenerationError);

    UIImage *thumbnailImage = thumbnailImageRef ? [[[UIImage alloc] initWithCGImage:thumbnailImageRef] autorelease] : nil;
     return thumbnailImage;
}