iOS - Automatically resize CVPixelBufferRef - iphone

Question

I am trying to crop and scale a CMSampleBufferRef based on user's inputs, on ratio, the below code takes a CMSampleBufferRef, convert it into a CVImageBufferRef and use CVPixelBuffer to crop the internal image based on its bytes. The goal of this process is to have a cropped and scaled CVPixelBufferRef to write to the video
- (CVPixelBufferRef)modifyImage:(CMSampleBufferRef) sampleBuffer {
#synchronized (self) {
CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer);
// Lock the image buffer
CVPixelBufferLockBaseAddress(imageBuffer,0);
// Get information about the image
uint8_t *baseAddress = (uint8_t *)CVPixelBufferGetBaseAddress(imageBuffer);
size_t bytesPerRow = CVPixelBufferGetBytesPerRow(imageBuffer);
size_t width = CVPixelBufferGetWidth(imageBuffer);
size_t height = CVPixelBufferGetHeight(imageBuffer);
CVPixelBufferRef pxbuffer;
NSDictionary *options = [NSDictionary dictionaryWithObjectsAndKeys:
[NSNumber numberWithBool:YES], kCVPixelBufferCGImageCompatibilityKey,
[NSNumber numberWithBool:YES], kCVPixelBufferCGBitmapContextCompatibilityKey,
[NSNumber numberWithInt:720], kCVPixelBufferWidthKey,
[NSNumber numberWithInt:1280], kCVPixelBufferHeightKey,
nil];
NSInteger tempWidth = (NSInteger) (width / ratio);
NSInteger tempHeight = (NSInteger) (height / ratio);
NSInteger baseAddressStart = 100 + 100 * bytesPerRow;
CVReturn status = CVPixelBufferCreateWithBytes(kCFAllocatorDefault, tempWidth, tempHeight, kCVPixelFormatType_32BGRA, &baseAddress[baseAddressStart], bytesPerRow, MyPixelBufferReleaseCallback, NULL, (CFDictionaryRef)options, &pxbuffer);
if (status != 0) {
CKLog(#"%d", status);
return NULL;
}
CVPixelBufferUnlockBaseAddress(imageBuffer,0);
return pxbuffer;
}
}
It all works fine, except that when I am trying to write it into the video's ouput using this method, it keeps receiving memory warning. It is fine if I keep the same ratio
- (void)writeBufferFrame:(CMSampleBufferRef)sampleBuffer pixelBuffer:(CVPixelBufferRef)pixelBuffer {
CMTime lastSampleTime = CMSampleBufferGetPresentationTimeStamp(sampleBuffer);
if(self.videoWriter.status != AVAssetWriterStatusWriting)
{
CKLog(#"%d", self.videoWriter.status);
[self.videoWriter startWriting];
[self.videoWriter startSessionAtSourceTime:lastSampleTime];
}
CVPixelBufferRef pxbuffer = [self modifyImage:sampleBuffer];
BOOL success = [self.avAdaptor appendPixelBuffer:pxbuffer withPresentationTime:lastSampleTime];
if (!success)
NSLog(#"Warning: Unable to write buffer to video");
}
I also tried with different approaches using CMSampleBufferRef and CGContext. If you can provide a solution for any approach here, I can give you the full score

Answer 1

Try to use kCVPixelBufferLock_ReadOnly flag in both calls to -CVPixelBufferLockBaseAddress and -CVPixelBufferUnlockBaseAddress.
And sometimes this issue can be solved by copying pixel buffer. Perform allocating once:
unsigned char *data = (unsigned char*)malloc(ySize * sizeof(unsigned char));
After that, copy data from pixelBuffer to data
size_t size = height * bytesPerRow;
memcpy(data, baseAddress, size);
After that, use data. Hope, that will help.