简单理解CVPixelBufferRef

CVPixelBufferRef简介

CVPixelBufferRef是像素缓冲区类型，像素缓冲区类型基于图像缓冲区类型；像素缓冲器实现了图像缓冲器的存储器存储。

/*!
    @typedef    CVPixelBufferRef
    @abstract   Based on the image buffer type. The pixel buffer implements the memory storage for an image buffer.

*/
typedef CVImageBufferRef CVPixelBufferRef;

由于CVPixelBufferRef是C中的对象，所以没有ARC内存管理，必须由开发者自己去管理引用计数，控制对象生命周期；

持有

/*!
    引用计数+1
    @function   CVPixelBufferRetain
    @abstract   Retains a CVPixelBuffer object
    @discussion Equivalent to CFRetain, but NULL safe
    @param      buffer A CVPixelBuffer object that you want to retain.
    @result     A CVPixelBuffer object that is the same as the passed in buffer.
*/
CV_EXPORT CVPixelBufferRef CV_NULLABLE CVPixelBufferRetain( CVPixelBufferRef CV_NULLABLE texture ) __OSX_AVAILABLE_STARTING(__MAC_10_4,__IPHONE_4_0);

释放

/*!
    引用计数-1
    @function   CVPixelBufferRelease
    @abstract   Releases a CVPixelBuffer object
    @discussion Equivalent to CFRelease, but NULL safe
    @param      buffer A CVPixelBuffer object that you want to release.
*/
CV_EXPORT void CVPixelBufferRelease( CV_RELEASES_ARGUMENT CVPixelBufferRef CV_NULLABLE texture ) __OSX_AVAILABLE_STARTING(__MAC_10_4,__IPHONE_4_0);

创建CVPixelBuffer

/*!
    创建CVPixelBuffer
    @function   CVPixelBufferCreate
    @abstract   Call to create a single PixelBuffer for a given size and pixelFormatType.
    @discussion Creates a single PixelBuffer for a given size and pixelFormatType. It allocates the necessary memory based on the pixel dimensions, pixelFormatType and extended pixels described in the pixelBufferAttributes. Not all parameters of the pixelBufferAttributes will be used here.
    @param      width   Width of the PixelBuffer in pixels.
    @param      height  Height of the PixelBuffer in pixels.
    @param  pixelFormatType     Pixel format indentified by its respective OSType.
    @param  pixelBufferAttributes      A dictionary with additional attributes for a pixel buffer. This parameter is optional. See BufferAttributeKeys for more details.
    @param      pixelBufferOut          The new pixel buffer will be returned here
    @result returns kCVReturnSuccess on success.
*/    
CV_EXPORT CVReturn CVPixelBufferCreate(
    CFAllocatorRef CV_NULLABLE allocator,
    size_t width,
    size_t height,
    OSType pixelFormatType,
    CFDictionaryRef CV_NULLABLE pixelBufferAttributes,
    CV_RETURNS_RETAINED_PARAMETER CVPixelBufferRef CV_NULLABLE * CV_NONNULL pixelBufferOut) __OSX_AVAILABLE_STARTING(__MAC_10_4,__IPHONE_4_0);

创建一个平面格式的CVPixelBuffer

/*!
    @function   CVPixelBufferCreateWithPlanarBytes
    @abstract   Call to create a single PixelBuffer in planar format for a given size and pixelFormatType based on a passed in piece of memory.
    @discussion Creates a single PixelBuffer for a given size and pixelFormatType. Not all parameters of the pixelBufferAttributes will be used here. It requires a release callback function that will be called, when the PixelBuffer gets destroyed so that the owner of the pixels can free the memory.
    @param      width           Width of the PixelBuffer in pixels
    @param      height          Height of the PixelBuffer in pixels
    @param      pixelFormatType     Pixel format indentified by its respective OSType.
    @param  dataPtr         Pass a pointer to a plane descriptor block, or NULL.
    @param  dataSize        pass size if planes are contiguous, NULL if not.
    @param  numberOfPlanes      Number of planes.
    @param  planeBaseAddress    Array of base addresses for the planes.
    @param  planeWidth      Array of plane widths.
    @param  planeHeight     Array of plane heights.
    @param  planeBytesPerRow    Array of plane bytesPerRow values.
    @param  releaseCallback     CVPixelBufferReleaseBytePointerCallback function that gets called when the PixelBuffer gets destroyed.
    @param  releaseRefCon       User data identifying the PixelBuffer for the release callback.
    @param  pixelBufferAttributes      A dictionary with additional attributes for a a pixel buffer. This parameter is optional. See PixelBufferAttributes for more details.
    @param      pixelBufferOut          The new pixel buffer will be returned here
    @result returns kCVReturnSuccess on success.
*/
CV_EXPORT CVReturn CVPixelBufferCreateWithPlanarBytes(
    CFAllocatorRef CV_NULLABLE allocator,
    size_t width,
    size_t height,
    OSType pixelFormatType,
    void * CV_NULLABLE dataPtr, // pass a pointer to a plane descriptor block, or NULL
    size_t dataSize, // pass size if planes are contiguous, NULL if not
    size_t numberOfPlanes,
    void * CV_NULLABLE planeBaseAddress[CV_NONNULL ],
    size_t planeWidth[CV_NONNULL ],
    size_t planeHeight[CV_NONNULL ],
    size_t planeBytesPerRow[CV_NONNULL ],
    CVPixelBufferReleasePlanarBytesCallback CV_NULLABLE releaseCallback,
    void * CV_NULLABLE releaseRefCon,
    CFDictionaryRef CV_NULLABLE pixelBufferAttributes,
    CV_RETURNS_RETAINED_PARAMETER CVPixelBufferRef CV_NULLABLE * CV_NONNULL pixelBufferOut) __OSX_AVAILABLE_STARTING(__MAC_10_4,__IPHONE_4_0);

• 像素格式类型pixelFormatType

RGB :
kCVPixelFormatType_32BGRA = 'BGRA',
kCVPixelFormatType_32BGRA = 'BGRA',
kCVPixelFormatType_32ABGR = 'ABGR',
kCVPixelFormatType_32RGBA = 'RGBA',
NV12 :
kCVPixelFormatType_420YpCbCr8BiPlanarVideoRange = '420v',
kCVPixelFormatType_420YpCbCr8BiPlanarFullRange = '420f',
YUV420P :
kCVPixelFormatType_420YpCbCr8Planar = 'y420',

kCVPixelFormatType_{长度|序列}{颜色空间}{Planar|BiPlanar}{VideoRange|FullRange}

从这里类型可以看出，YUV格式和RGB格式都是可以创建成CVPixelBuffer；

那么拿到CVPixelBufferRef后，如果要显示的话， 我们可以通过CVPixelBufferRef转成UIImage，或者通过绘制纹理的形式展示。

后续深入了解了这些之后，再来补充更多细节；