我从系统API接收到了一个包含非线性像素的CMSampleBufferRef，其中包含平面像素（如420f，也称为kCVPixelFormatType_420YpCbCr8BiPlanarVideoRange，又称yCbCr或YUV）。
在将视频数据发送到VideoToolkit进行h264编码之前，我想对此进行一些操作（例如绘制一些文本、添加水印、旋转图像等），但同时希望操作高效且实时。然而，平面图像数据看起来非常混乱 - 它们有色度平面和亮度平面，它们的大小不同... 在字节级别处理这个问题似乎需要花费很多力气。
我可能可以使用一个CGContextRef并直接在像素上绘制，但据我所知它只支持RGBA像素。您有什么建议可以尽可能少地复制数据，并且代码行数尽量少？
CGBitmapContextRef只能绘制类似于32ARGB的图像，这意味着您需要创建ARGB（或RGBA）缓冲区，然后找到一种快速将YUV像素转移到此ARGB表面的方法。该过程包括使用CoreImage，通过池自制CVPixelBufferRef，引用您自制像素缓冲区的CGBitmapContextRef，然后重新创建一个类似于输入缓冲区但引用输出像素的CMSampleBufferRef。换句话说，
CIImage中。CVPixelBufferPool。在实时情况下，不要创建没有池的CVPixelBuffer：如果生产者太快，则会耗尽内存；如果您不重复使用缓冲区，则会分段RAM；这是浪费周期。CIContext，并在缓冲区之间共享。它不包含外部状态，但文档表示，在每个帧上重新创建它非常昂贵。CMVideoFormatDescriptionRefCGBitmapContext和CoreVideo都能很好地处理的格式：{
CGPixelBufferPoolRef *_pool;
CGSize _poolBufferDimensions;
}
- (void)_processSampleBuffer:(CMSampleBufferRef)inputBuffer
{
// 1. Input data
CVPixelBufferRef inputPixels = CMSampleBufferGetImageBuffer(inputBuffer);
CIImage *inputImage = [CIImage imageWithCVPixelBuffer:inputPixels];
// 2. Create a new pool if the old pool doesn't have the right format.
CGSize bufferDimensions = {CVPixelBufferGetWidth(inputPixels), CVPixelBufferGetHeight(inputPixels)};
if(!_pool || !CGSizeEqualToSize(bufferDimensions, _poolBufferDimensions)) {
if(_pool) {
CFRelease(_pool);
}
OSStatus ok0 = CVPixelBufferPoolCreate(NULL,
NULL, // pool attrs
(__bridge CFDictionaryRef)(@{
(id)kCVPixelBufferPixelFormatTypeKey: @(kCVPixelFormatType_32ARGB),
(id)kCVPixelBufferWidthKey: @(bufferDimensions.width),
(id)kCVPixelBufferHeightKey: @(bufferDimensions.height),
}), // buffer attrs
&_pool
);
_poolBufferDimensions = bufferDimensions;
assert(ok0 == noErr);
}
// 4. Create pixel buffer
CVPixelBufferRef outputPixels;
OSStatus ok1 = CVPixelBufferPoolCreatePixelBufferWithAuxAttributes(NULL,
_pool,
(__bridge CFDictionaryRef)@{
// Opt to fail buffer creation in case of slow buffer consumption
// rather than to exhaust all memory.
(__bridge id)kCVPixelBufferPoolAllocationThresholdKey: @20
}, // aux attributes
&outputPixels
);
if(ok1 == kCVReturnWouldExceedAllocationThreshold) {
// Dropping frame because consumer is too slow
return;
}
assert(ok1 == noErr);
// 5, 6. Graphics context to draw in
CGColorSpaceRef deviceColors = CGColorSpaceCreateDeviceRGB();
OSStatus ok2 = CVPixelBufferLockBaseAddress(outputPixels, 0);
assert(ok2 == noErr);
CGContextRef cg = CGBitmapContextCreate(
CVPixelBufferGetBaseAddress(outputPixels), // bytes
CVPixelBufferGetWidth(inputPixels), CVPixelBufferGetHeight(inputPixels), // dimensions
8, // bits per component
CVPixelBufferGetBytesPerRow(outputPixels), // bytes per row
deviceColors, // color space
kCGImageAlphaPremultipliedFirst // bitmap info
);
CFRelease(deviceColors);
assert(cg != NULL);
// 7
[_imageContext render:inputImage toCVPixelBuffer:outputPixels];
// 8. DRAW
CGContextSetRGBFillColor(cg, 0.5, 0, 0, 1);
CGContextSetTextDrawingMode(cg, kCGTextFill);
NSAttributedString *text = [[NSAttributedString alloc] initWithString:@"Hello world" attributes:NULL];
CTLineRef line = CTLineCreateWithAttributedString((__bridge CFAttributedStringRef)text);
CTLineDraw(line, cg);
CFRelease(line);
// 9. Unlock and stop drawing
CFRelease(cg);
CVPixelBufferUnlockBaseAddress(outputPixels, 0);
// 10. Timings
CMSampleTimingInfo timingInfo;
OSStatus ok4 = CMSampleBufferGetSampleTimingInfo(inputBuffer, 0, &timingInfo);
assert(ok4 == noErr);
// 11. VIdeo format
CMVideoFormatDescriptionRef videoFormat;
OSStatus ok5 = CMVideoFormatDescriptionCreateForImageBuffer(NULL, outputPixels, &videoFormat);
assert(ok5 == noErr);
// 12. Output sample buffer
CMSampleBufferRef outputBuffer;
OSStatus ok3 = CMSampleBufferCreateForImageBuffer(NULL, // allocator
outputPixels, // image buffer
YES, // data ready
NULL, // make ready callback
NULL, // make ready refcon
videoFormat,
&timingInfo, // timing info
&outputBuffer // out
);
assert(ok3 == noErr);
[_consumer consumeSampleBuffer:outputBuffer];
CFRelease(outputPixels);
CFRelease(videoFormat);
CFRelease(outputBuffer);
}