iOS - 自动调整 CVPixelBufferRef 的大小

Question

我正在尝试根据用户的输入裁剪和缩放CMSampleBufferRef，在ratio 上，以下代码采用 CMSampleBufferRef，将其转换为 CVImageBufferRef 并使用 CVPixelBuffer 根据其字节裁剪内部图像。这个过程的目标是有一个裁剪和缩放的 CVPixelBufferRef 来写入视频

- (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;
    }
}

一切正常，除了当我尝试使用此方法将其写入视频输出时，它不断收到内存警告。如果我保持相同的比例就可以了

- (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");
}

我还尝试了使用CMSampleBufferRef 和CGContext 的不同方法。如果您可以在这里为任何方法提供解决方案，我可以给您满分

Answer 1

尝试在调用 -CVPixelBufferLockBaseAddress 和 -CVPixelBufferUnlockBaseAddress 时使用 kCVPixelBufferLock_ReadOnly 标志。 有时这个问题可以通过复制像素缓冲区来解决。执行一次分配：

unsigned char *data = (unsigned char*)malloc(ySize * sizeof(unsigned char));

之后，将数据从pixelBuffer复制到data

size_t size = height * bytesPerRow;

memcpy(数据, baseAddress, 大小);

之后，使用数据。希望，这会有所帮助。