ios取出视频的每一帧图片（关键帧，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];
         }
     }];

如何取得第一帧

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;