Question

我正在尝试将CMSampleBufferRef中的图片裁剪为特定尺寸。我正在制作5个步骤 - 1.从PixelBuffer获取SampleBuffer 2.将PixelBuffer转换为CIImage 3.裁剪CIImage 4.渲染CIImage返回PixelBuffer 5.将PixelBuffer附加到SampleBuffer。到目前为止，我遇到了第4步的问题 - 将图像渲染回PixelBuffer（无法检查超出此点）没有任何内容呈现给缓冲区（我使用相同的CIImage imageWithCVPixelBuffer检查它并获取NULL作为返回）。非常感谢任何提示或帮助。

CGRect cropRect = CGRectMake(0, 0, 640, 480);

CIImage *ciImage = [CIImage imageWithCVPixelBuffer:(CVPixelBufferRef)CMSampleBufferGetImageBuffer(sampleBuffer)]; //options: [NSDictionary dictionaryWithObjectsAndKeys:[NSNull null], kCIImageColorSpace, nil]];
ciImage = [ciImage imageByCroppingToRect:cropRect];    

CVPixelBufferRef pixelBuffer;
CVPixelBufferCreate(kCFAllocatorSystemDefault, 640, 480, kCVPixelFormatType_32BGRA, NULL, &pixelBuffer);

CVPixelBufferLockBaseAddress( pixelBuffer, 0 );

CIContext * ciContext = [CIContext contextWithOptions: nil];
[ciContext render:ciImage toCVPixelBuffer:pixelBuffer];
CVPixelBufferUnlockBaseAddress( pixelBuffer, 0 );

CMSampleTimingInfo sampleTime = {
    .duration = CMSampleBufferGetDuration(sampleBuffer),
    .presentationTimeStamp = CMSampleBufferGetPresentationTimeStamp(sampleBuffer),
    .decodeTimeStamp = CMSampleBufferGetDecodeTimeStamp(sampleBuffer)
};

CMVideoFormatDescriptionRef videoInfo = NULL;
CMVideoFormatDescriptionCreateForImageBuffer(kCFAllocatorDefault, pixelBuffer, &videoInfo);

CMSampleBufferRef oBuf;
CMSampleBufferCreateForImageBuffer(kCFAllocatorDefault, pixelBuffer, true, NULL, NULL, videoInfo, &sampleTime, &oBuf);

Answer 1

所以我找到了我遇到问题的原因。显然我必须在初始化像素缓冲区时添加kCVPixelBufferIOSurfacePropertiesKey键，方法是创建字典并将其传递给初始化程序。如果有人遇到这个问题，这是一个代码：

CFDictionaryRef empty; // empty value for attr value.
CFMutableDictionaryRef attrs;
empty = CFDictionaryCreate(kCFAllocatorDefault, // our empty IOSurface properties dictionary
                           NULL,
                           NULL,
                           0,
                           &kCFTypeDictionaryKeyCallBacks,
                           &kCFTypeDictionaryValueCallBacks);
attrs = CFDictionaryCreateMutable(kCFAllocatorDefault,
                                  1,
                                  &kCFTypeDictionaryKeyCallBacks,
                                  &kCFTypeDictionaryValueCallBacks);

CFDictionarySetValue(attrs,
                     kCVPixelBufferIOSurfacePropertiesKey,
                     empty);

然后你只需将这个字典作为参数传递给CVPixelBufferCreate

我在这里找到了这个解决方案：http://allmybrain.com/2011/12/08/rendering-to-a-texture-with-ios-5-texture-cache-api/

裁剪CMSampleBufferRef

1 个答案: