converting CMSampleBufferRef to UIImage - uiimage

Question

i always get : CGImageCreate: invalid image size: 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");}];
the imageFromSampleBuffer comes directly from 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;
}
i try to get the length and width, basically it will print out the size of the sample buffer, knowing that the buffer itself is not inexistant, but i get no UIImage

Answer 1

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

Answer 2

I understand you want to read first image from all your local videos?
You can use simple way to do all of this.
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");}];