Convert UIImage to CMSampleBufferRef

Question

I am doing video recording using AVFoundation. I have to crop the video to 320x280. I am getting the CMSampleBufferRef and converting it to UIImage using the below code.

CGImageRef _cgImage = [self imageFromSampleBuffer:sampleBuffer];
UIImage *_uiImage = [UIImage imageWithCGImage:_cgImage];
CGImageRelease(_cgImage);
_uiImage = [_uiImage resizedImageWithSize:CGSizeMake(320, 280)];

CMSampleBufferRef croppedBuffer = /* NEED HELP WITH THIS */

[_videoInput appendSampleBuffer:sampleBuffer]; 
// _videoInput is a AVAssetWriterInput

The imageFromSampleBuffer: method looks like this:

- (CGImageRef) imageFromSampleBuffer:(CMSampleBufferRef) sampleBuffer // Create a CGImageRef from sample buffer data
{
    CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer);
    CVPixelBufferLockBaseAddress(imageBuffer,0);        // Lock the image buffer

    uint8_t *baseAddress = (uint8_t *)CVPixelBufferGetBaseAddressOfPlane(imageBuffer, 0);   // Get information of the image
    size_t bytesPerRow = CVPixelBufferGetBytesPerRow(imageBuffer);
    size_t width = CVPixelBufferGetWidth(imageBuffer);
    size_t height = CVPixelBufferGetHeight(imageBuffer);
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();

    CGContextRef newContext = CGBitmapContextCreate(baseAddress, width, height, 8, bytesPerRow, colorSpace, kCGBitmapByteOrder32Little | kCGImageAlphaPremultipliedFirst);
    CGImageRef newImage = CGBitmapContextCreateImage(newContext);
    CGContextRelease(newContext);

    CGColorSpaceRelease(colorSpace);
    CVPixelBufferUnlockBaseAddress(imageBuffer,0);
    /* CVBufferRelease(imageBuffer); */  // do not call this!

    return newImage;
}

Now I have to convert the resized image back to CMSampleBufferRef to write in AVAssetWriterInput.

How do I convert UIImage to CMSampleBufferRef?

Thanks everyone!

Answer 1

While you could create your own Core Media sample buffers from scratch, it's probably easier to use a AVPixelBufferAdaptor.

You describe the source pixel buffer format in the inputSettings dictionary and pass that to the adaptor initializer:

NSMutableDictionary* inputSettingsDict = [NSMutableDictionary dictionary];
[inputSettingsDict setObject:[NSNumber numberWithInt:pixelFormat] forKey:(NSString*)kCVPixelBufferPixelFormatTypeKey];
[inputSettingsDict setObject:[NSNumber numberWithUnsignedInteger:(NSUInteger)(image.uncompressedSize/image.rect.size.height)] forKey:(NSString*)kCVPixelBufferBytesPerRowAlignmentKey];
[inputSettingsDict setObject:[NSNumber numberWithDouble:image.rect.size.width] forKey:(NSString*)kCVPixelBufferWidthKey];
[inputSettingsDict setObject:[NSNumber numberWithDouble:image.rect.size.height] forKey:(NSString*)kCVPixelBufferHeightKey];
[inputSettingsDict setObject:[NSNumber numberWithBool:YES] forKey:(NSString*)kCVPixelBufferCGImageCompatibilityKey];
[inputSettingsDict setObject:[NSNumber numberWithBool:YES] forKey:(NSString*)kCVPixelBufferCGBitmapContextCompatibilityKey];
AVAssetWriterInputPixelBufferAdaptor* pixelBufferAdapter = [[AVAssetWriterInputPixelBufferAdaptor alloc] initWithAssetWriterInput:assetWriterInput sourcePixelBufferAttributes:inputSettingsDict];

You can then append CVPixelBuffers to your adaptor:

[pixelBufferAdapter appendPixelBuffer:completePixelBuffer withPresentationTime:pixelBufferTime]

The pixelbufferAdaptor accepts CVPixelBuffers, so you have to convert your UIImages to pixelBuffers, which is described here: https://stackoverflow.com/a/3742212/100848
Pass the CGImage property of your UIImage to newPixelBufferFromCGImage.

Answer 2

This is a function that I use in my GPUImage framework to resize an incoming CMSampleBufferRef and place the scaled results within a CVPixelBufferRef that you provide:

void GPUImageCreateResizedSampleBuffer(CVPixelBufferRef cameraFrame, CGSize finalSize, CMSampleBufferRef *sampleBuffer)
{
    // CVPixelBufferCreateWithPlanarBytes for YUV input

    CGSize originalSize = CGSizeMake(CVPixelBufferGetWidth(cameraFrame), CVPixelBufferGetHeight(cameraFrame));

    CVPixelBufferLockBaseAddress(cameraFrame, 0);
    GLubyte *sourceImageBytes =  CVPixelBufferGetBaseAddress(cameraFrame);
    CGDataProviderRef dataProvider = CGDataProviderCreateWithData(NULL, sourceImageBytes, CVPixelBufferGetBytesPerRow(cameraFrame) * originalSize.height, NULL);
    CGColorSpaceRef genericRGBColorspace = CGColorSpaceCreateDeviceRGB();
    CGImageRef cgImageFromBytes = CGImageCreate((int)originalSize.width, (int)originalSize.height, 8, 32, CVPixelBufferGetBytesPerRow(cameraFrame), genericRGBColorspace, kCGBitmapByteOrder32Little | kCGImageAlphaPremultipliedFirst, dataProvider, NULL, NO, kCGRenderingIntentDefault);

    GLubyte *imageData = (GLubyte *) calloc(1, (int)finalSize.width * (int)finalSize.height * 4);

    CGContextRef imageContext = CGBitmapContextCreate(imageData, (int)finalSize.width, (int)finalSize.height, 8, (int)finalSize.width * 4, genericRGBColorspace,  kCGBitmapByteOrder32Little | kCGImageAlphaPremultipliedFirst);
    CGContextDrawImage(imageContext, CGRectMake(0.0, 0.0, finalSize.width, finalSize.height), cgImageFromBytes);
    CGImageRelease(cgImageFromBytes);
    CGContextRelease(imageContext);
    CGColorSpaceRelease(genericRGBColorspace);
    CGDataProviderRelease(dataProvider);

    CVPixelBufferRef pixel_buffer = NULL;
    CVPixelBufferCreateWithBytes(kCFAllocatorDefault, finalSize.width, finalSize.height, kCVPixelFormatType_32BGRA, imageData, finalSize.width * 4, stillImageDataReleaseCallback, NULL, NULL, &pixel_buffer);
    CMVideoFormatDescriptionRef videoInfo = NULL;
    CMVideoFormatDescriptionCreateForImageBuffer(NULL, pixel_buffer, &videoInfo);

    CMTime frameTime = CMTimeMake(1, 30);
    CMSampleTimingInfo timing = {frameTime, frameTime, kCMTimeInvalid};

    CMSampleBufferCreateForImageBuffer(kCFAllocatorDefault, pixel_buffer, YES, NULL, NULL, videoInfo, &timing, sampleBuffer);
    CFRelease(videoInfo);
    CVPixelBufferRelease(pixel_buffer);
}

It doesn't take you all the way to creating a CMSampleBufferRef, but as weichsel points out, you only need the CVPixelBufferRef for encoding the video.

However, if what you really want to do here is crop video and record it, going to and from a UIImage is going to be a very slow way to do this. Instead, may I recommend looking into using something like GPUImage to capture video with a GPUImageVideoCamera input (or GPUImageMovie if cropping a previously recorded movie), feeding that into a GPUImageCropFilter, and taking the result to a GPUImageMovieWriter. That way, the video never touches Core Graphics and hardware acceleration is used as much as possible. It will be a lot faster than what you describe above.

Answer 3

- (CVPixelBufferRef)CVPixelBufferRefFromUiImage:(UIImage *)img {

    CGSize size = img.size;
    CGImageRef image = [img CGImage];

    NSDictionary *options = [NSDictionary dictionaryWithObjectsAndKeys:
                             [NSNumber numberWithBool:YES], kCVPixelBufferCGImageCompatibilityKey,
                             [NSNumber numberWithBool:YES], kCVPixelBufferCGBitmapContextCompatibilityKey, nil];
    CVPixelBufferRef pxbuffer = NULL;
    CVReturn status = CVPixelBufferCreate(kCFAllocatorDefault, size.width, size.height, kCVPixelFormatType_32ARGB, (__bridge CFDictionaryRef) options, &pxbuffer);

    NSParameterAssert(status == kCVReturnSuccess && pxbuffer != NULL);

    CVPixelBufferLockBaseAddress(pxbuffer, 0);
    void *pxdata = CVPixelBufferGetBaseAddress(pxbuffer);
    NSParameterAssert(pxdata != NULL);

    CGColorSpaceRef rgbColorSpace = CGColorSpaceCreateDeviceRGB();
    CGContextRef context = CGBitmapContextCreate(pxdata, size.width, size.height, 8, 4*size.width, rgbColorSpace, kCGImageAlphaPremultipliedFirst);
    NSParameterAssert(context);

    CGContextDrawImage(context, CGRectMake(0, 0, CGImageGetWidth(image), CGImageGetHeight(image)), image);

    CGColorSpaceRelease(rgbColorSpace);
    CGContextRelease(context);

    CVPixelBufferUnlockBaseAddress(pxbuffer, 0);

    return pxbuffer;
}