iOS - Automatically resize CVPixelBufferRef

问题

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

回答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.

来源：https://stackoverflow.com/questions/8561456/ios-automatically-resize-cvpixelbufferref

标签

iphone

objective-c

ios

avfoundation

cmsamplebufferref