Question

我总是得到：CGImageCreate：图片大小无效：0 x 0。

ALAssetsLibrary *library = [[ALAssetsLibrary alloc] init];

 // Enumerate just the photos and videos group by using ALAssetsGroupSavedPhotos.
 [library enumerateGroupsWithTypes:ALAssetsGroupSavedPhotos
         usingBlock:^(ALAssetsGroup *group, BOOL *stop) {

  // Within the group enumeration block, filter to enumerate just videos.
  [group setAssetsFilter:[ALAssetsFilter allVideos]];

  // For this example, we're only interested in the first item.
  [group enumerateAssetsAtIndexes:[NSIndexSet indexSetWithIndex:0]
        options:0
        usingBlock:^(ALAsset *alAsset, NSUInteger index, BOOL *innerStop) {

         // The end of the enumeration is signaled by asset == nil.
         if (alAsset) {
          ALAssetRepresentation *representation = [[alAsset defaultRepresentation] retain];
          NSURL *url = [representation url];
          AVURLAsset *avAsset = [[AVURLAsset URLAssetWithURL:url options:nil] retain];
          AVAssetReader *assetReader = [[AVAssetReader assetReaderWithAsset:avAsset error:nil] retain];
          NSArray *tracks = [avAsset tracksWithMediaType:AVMediaTypeVideo];
          AVAssetTrack *videoTrack = [tracks objectAtIndex:0];
          AVAssetReaderTrackOutput *assetReaderOutput = [[AVAssetReaderTrackOutput assetReaderTrackOutputWithTrack:videoTrack outputSettings:nil] retain];
          if (![assetReader canAddOutput:assetReaderOutput]) {printf("could not read reader output\n");}
          [assetReader addOutput:assetReaderOutput];
          [assetReader startReading];
          CMSampleBufferRef nextBuffer = [assetReaderOutput copyNextSampleBuffer];
          UIImage* image = imageFromSampleBuffer(nextBuffer);              
         }
        }];
 }
 failureBlock: ^(NSError *error) {NSLog(@"No groups");}];

imageFromSampleBuffer直接来自apple：

    UIImage* imageFromSampleBuffer(CMSampleBufferRef nextBuffer) {

 CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(nextBuffer);
 printf("total size:%u\n",CMSampleBufferGetTotalSampleSize(nextBuffer));
 // Lock the base address of the pixel buffer.
 //CVPixelBufferLockBaseAddress(imageBuffer,0);

 // Get the number of bytes per row for the pixel buffer.
 size_t bytesPerRow = CVPixelBufferGetBytesPerRow(imageBuffer);
 // Get the pixel buffer width and height.
 size_t width = CVPixelBufferGetWidth(imageBuffer);
 size_t height = CVPixelBufferGetHeight(imageBuffer);
 printf("b:%d w:%d h:%d\n",bytesPerRow,width,height);

 // Create a device-dependent RGB color space.
 static CGColorSpaceRef colorSpace = NULL;
 if (colorSpace == NULL) {
  colorSpace = CGColorSpaceCreateDeviceRGB();
  if (colorSpace == NULL) {
   // Handle the error appropriately.
   return nil;
  }
 }

 // Get the base address of the pixel buffer.
 void *baseAddress = CVPixelBufferGetBaseAddress(imageBuffer);
 // Get the data size for contiguous planes of the pixel buffer.
 size_t bufferSize = CVPixelBufferGetDataSize(imageBuffer);

 // Create a Quartz direct-access data provider that uses data we supply.
 CGDataProviderRef dataProvider =
 CGDataProviderCreateWithData(NULL, baseAddress, bufferSize, NULL);
 // Create a bitmap image from data supplied by the data provider.
 CGImageRef cgImage =
 CGImageCreate(width, height, 8, 32, bytesPerRow,
      colorSpace, kCGImageAlphaNoneSkipFirst | kCGBitmapByteOrder32Little,
      dataProvider, NULL, true, kCGRenderingIntentDefault);
 CGDataProviderRelease(dataProvider);

 // Create and return an image object to represent the Quartz image.
 UIImage *image = [UIImage imageWithCGImage:cgImage];
 CGImageRelease(cgImage);

 CVPixelBufferUnlockBaseAddress(imageBuffer, 0);

 return image;
}

我试着获得长度和宽度，基本上它会打印出样本缓冲区的大小，知道缓冲区本身不是不存在的，但我得不到UIImage

Answer 1

for AVAssetReaderTrackOutput * assetReaderOutput ...

NSMutableDictionary *outputSettings = [NSMutableDictionary dictionary];
[outputSettings setObject: [NSNumber numberWithInt:kCVPixelFormatType_32BGRA] forKey:(NSString*)kCVPixelBufferPixelFormatTypeKey];

Answer 2

我了解您想要阅读所有本地视频中的第一张图片？您可以使用简单的方法来完成所有这些。

 ALAssetsLibrary *library = [[ALAssetsLibrary alloc] init];

 // Enumerate just the photos and videos group by using ALAssetsGroupSavedPhotos.
 [library enumerateGroupsWithTypes:ALAssetsGroupSavedPhotos
         usingBlock:^(ALAssetsGroup *group, BOOL *stop) {

  // Within the group enumeration block, filter to enumerate just videos.
  [group setAssetsFilter:[ALAssetsFilter allVideos]];

  // For this example, we're only interested in the first item.
  [group enumerateAssetsAtIndexes:[NSIndexSet indexSetWithIndex:0]
        options:0
        usingBlock:^(ALAsset *alAsset, NSUInteger index, BOOL *innerStop) {

         // The end of the enumeration is signaled by asset == nil.
         if (alAsset) {
          ALAssetRepresentation *representation = [[alAsset defaultRepresentation] retain];
          NSURL *url = [representation url];
          AVURLAsset *avAsset = [[AVURLAsset URLAssetWithURL:url options:nil] retain];
          AVAssetImageGenerator *imageGenerator = [[AVAssetImageGenerator alloc] initWithAsset:avAsset];
          CMTime thumbTime = CMTimeMakeWithSeconds(1, 30);

          NSError *error;
          CMTime actualTime;
          [imageGenerator setMaximumSize:MAXSIZE];
          CGImageRef imageRef = [imageGenerator copyCGImageAtTime:thumbTime actualTime:&actualTime error:&error];             
         }
        }];
 }
 failureBlock: ^(NSError *error) {NSLog(@"No groups");}];

将CMSampleBufferRef转换为UIImage

2 个答案: