Repeated Scene items in iOS YUV video capturing output - iphone

Question

I capture a video and handle the resulting YUV frames.
the output looks like the following:
Although it appears normally on my phone's screen. But my peer receives it like that img above.
Every item is repeated and shifted by some value horizontally and vertically
My captured video is 352x288 and my YPixelCount = 101376, UVPixelCount = YPIXELCOUNT/4
Any clue to solve this or a starting point to understand how to handle YUV video frames on iOS ?
NSNumber* recorderValue = [NSNumber numberWithUnsignedInt:kCVPixelFormatType_420YpCbCr8BiPlanarVideoRange];
[videoRecorderSession setSessionPreset:AVCaptureSessionPreset352x288];
And this is the captureOutput function
- (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection{
if(CMSampleBufferIsValid(sampleBuffer) && CMSampleBufferDataIsReady(sampleBuffer) && ([self isQueueStopped] == FALSE))
{
CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer);
CVPixelBufferLockBaseAddress(imageBuffer,0);
UInt8 *baseAddress[3] = {NULL,NULL,NULL};
uint8_t *yPlaneAddress = (uint8_t *)CVPixelBufferGetBaseAddressOfPlane(imageBuffer,0);
UInt32 yPixelCount = CVPixelBufferGetWidthOfPlane(imageBuffer,0) * CVPixelBufferGetHeightOfPlane(imageBuffer,0);
uint8_t *uvPlaneAddress = (uint8_t *)CVPixelBufferGetBaseAddressOfPlane(imageBuffer,1);
UInt32 uvPixelCount = CVPixelBufferGetWidthOfPlane(imageBuffer,1) * CVPixelBufferGetHeightOfPlane(imageBuffer,1);
UInt32 p,q,r;
p=q=r=0;
memcpy(uPointer, uvPlaneAddress, uvPixelCount);
memcpy(vPointer, uvPlaneAddress+uvPixelCount, uvPixelCount);
memcpy(yPointer,yPlaneAddress,yPixelCount);
baseAddress[0] = (UInt8*)yPointer;
baseAddress[1] = (UInt8*)uPointer;
baseAddress[2] = (UInt8*)vPointer;
CVPixelBufferUnlockBaseAddress(imageBuffer,0);
}
}
Is there anything wrong with the above code ?

Answer 1

Your code doesn't look to0 bad. I can see two mistakes and one potential problem:
The uvPixelCount is incorrect. The YUV 420 format means that there is color information for each 2 by 2 pixel block. So the correct count is:
uvPixelCount = (width / 2) * (height / 2);
You write something about yPixelCount / 4, but I cannot see that in your code.
The UV information is interleaved, i.e. the second plane alternatingly contains a U and a V value. Or put differently: there's a U value on all even byte addresses and a V value on all odd byte addresses. If you really need to separate the U and V information, memcpy won't do.
There can be some extra bytes after each pixel row. You should use CVPixelBufferGetBytesPerRowOfPlane(imageBuffer, 0) to get the number of bytes between two rows. As a consequence, a single memcpy won't do. Instead you need to copy each pixel row separately to get rid of the extra bytes between the rows.
All these things only explain part of the resulting image. The remaining parts are probably due to differences between your code and what the receiving peer expect. You did't write anything about that? Does the peer really need separated U and V values? Does it you 4:2:0 compression as well? Does it you video range instead of full range as well?
If you provide more information, I can give your more hints.