什么是iOS中的CVPixelBuffer？

根据Apple文档,它是存储在主存储器中的图像,但这些图像如何用于制作电影？

CVPixelBuffer是CoreVideo内部格式的原始图像格式(因此CoreVideo的'CV'前缀).CoreVideo是一个iOS框架.

它可以包含以下格式之一的图像(取决于其来源):

/*
CoreVideo pixel format type constants.
CoreVideo does not provide support for all of these formats; this list just defines their names.
*/
#if COREVIDEO_USE_DERIVED_ENUMS_FOR_CONSTANTS
enum : OSType
#else
enum
#endif
{
  kCVPixelFormatType_1Monochrome    = 0x00000001, /* 1 bit indexed */
  kCVPixelFormatType_2Indexed       = 0x00000002, /* 2 bit indexed */
  kCVPixelFormatType_4Indexed       = 0x00000004, /* 4 bit indexed */
  kCVPixelFormatType_8Indexed       = 0x00000008, /* 8 bit indexed */
  kCVPixelFormatType_1IndexedGray_WhiteIsZero = 0x00000021, /* 1 bit indexed gray, white is zero */
  kCVPixelFormatType_2IndexedGray_WhiteIsZero = 0x00000022, /* 2 bit indexed gray, white is zero */
  kCVPixelFormatType_4IndexedGray_WhiteIsZero = 0x00000024, /* 4 bit indexed gray, white is zero */
  kCVPixelFormatType_8IndexedGray_WhiteIsZero = 0x00000028, /* 8 bit indexed gray, white is zero */
  kCVPixelFormatType_16BE555        = 0x00000010, /* 16 bit BE RGB 555 */
  kCVPixelFormatType_16LE555        = 'L555',     /* 16 bit LE RGB 555 */
  kCVPixelFormatType_16LE5551       = '5551',     /* 16 bit LE RGB 5551 */
  kCVPixelFormatType_16BE565        = 'B565',     /* 16 bit BE RGB 565 */
  kCVPixelFormatType_16LE565        = 'L565',     /* 16 bit LE RGB 565 */
  kCVPixelFormatType_24RGB          = 0x00000018, /* 24 bit RGB */
  kCVPixelFormatType_24BGR          = '24BG',     /* 24 bit BGR */
  kCVPixelFormatType_32ARGB         = 0x00000020, /* 32 bit ARGB */
  kCVPixelFormatType_32BGRA         = 'BGRA',     /* 32 bit BGRA */
  kCVPixelFormatType_32ABGR         = 'ABGR',     /* 32 bit ABGR */
  kCVPixelFormatType_32RGBA         = 'RGBA',     /* 32 bit RGBA */
  kCVPixelFormatType_64ARGB         = 'b64a',     /* 64 bit ARGB, 16-bit big-endian samples */
  kCVPixelFormatType_48RGB          = 'b48r',     /* 48 bit RGB, 16-bit big-endian samples */
  kCVPixelFormatType_32AlphaGray    = 'b32a',     /* 32 bit AlphaGray, 16-bit big-endian samples, black is zero */
  kCVPixelFormatType_16Gray         = 'b16g',     /* 16 bit Grayscale, 16-bit big-endian samples, black is zero */
  kCVPixelFormatType_30RGB          = 'R10k',     /* 30 bit RGB, 10-bit big-endian samples, 2 unused padding bits (at least significant end). */
  kCVPixelFormatType_422YpCbCr8     = '2vuy',     /* Component Y'CbCr 8-bit 4:2:2, ordered Cb Y'0 Cr Y'1 */
  kCVPixelFormatType_4444YpCbCrA8   = 'v408',     /* Component Y'CbCrA 8-bit 4:4:4:4, ordered Cb Y' Cr A */
  kCVPixelFormatType_4444YpCbCrA8R  = 'r408',     /* Component Y'CbCrA 8-bit 4:4:4:4, rendering format. full range alpha, zero biased YUV, ordered A Y' Cb Cr */
  kCVPixelFormatType_4444AYpCbCr8   = 'y408',     /* Component Y'CbCrA 8-bit 4:4:4:4, ordered A Y' Cb Cr, full range alpha, video range Y'CbCr. */
  kCVPixelFormatType_4444AYpCbCr16  = 'y416',     /* Component Y'CbCrA 16-bit 4:4:4:4, ordered A Y' Cb Cr, full range alpha, video range Y'CbCr, 16-bit little-endian samples. */
  kCVPixelFormatType_444YpCbCr8     = 'v308',     /* Component Y'CbCr 8-bit 4:4:4 */
  kCVPixelFormatType_422YpCbCr16    = 'v216',     /* Component Y'CbCr 10,12,14,16-bit 4:2:2 */
  kCVPixelFormatType_422YpCbCr10    = 'v210',     /* Component Y'CbCr 10-bit 4:2:2 */
  kCVPixelFormatType_444YpCbCr10    = 'v410',     /* Component Y'CbCr 10-bit 4:4:4 */
  kCVPixelFormatType_420YpCbCr8Planar = 'y420',   /* Planar Component Y'CbCr 8-bit 4:2:0.  baseAddr points to a big-endian CVPlanarPixelBufferInfo_YCbCrPlanar struct */
  kCVPixelFormatType_420YpCbCr8PlanarFullRange    = 'f420',   /* Planar Component Y'CbCr 8-bit 4:2:0, full range.  baseAddr points to a big-endian CVPlanarPixelBufferInfo_YCbCrPlanar struct */
  kCVPixelFormatType_422YpCbCr_4A_8BiPlanar = 'a2vy', /* First plane: Video-range Component Y'CbCr 8-bit 4:2:2, ordered Cb Y'0 Cr Y'1; second plane: alpha 8-bit 0-255 */
  kCVPixelFormatType_420YpCbCr8BiPlanarVideoRange = '420v', /* Bi-Planar Component Y'CbCr 8-bit 4:2:0, video-range (luma=[16,235] chroma=[16,240]).  baseAddr points to a big-endian CVPlanarPixelBufferInfo_YCbCrBiPlanar struct */
  kCVPixelFormatType_420YpCbCr8BiPlanarFullRange  = '420f', /* Bi-Planar Component Y'CbCr 8-bit 4:2:0, full-range (luma=[0,255] chroma=[1,255]).  baseAddr points to a big-endian CVPlanarPixelBufferInfo_YCbCrBiPlanar struct */ 
  kCVPixelFormatType_422YpCbCr8_yuvs = 'yuvs',     /* Component Y'CbCr 8-bit 4:2:2, ordered Y'0 Cb Y'1 Cr */
  kCVPixelFormatType_422YpCbCr8FullRange = 'yuvf', /* Component Y'CbCr 8-bit 4:2:2, full range, ordered Y'0 Cb Y'1 Cr */
  kCVPixelFormatType_OneComponent8  = 'L008',     /* 8 bit one component, black is zero */
  kCVPixelFormatType_TwoComponent8  = '2C08',     /* 8 bit two component, black is zero */
  kCVPixelFormatType_30RGBLEPackedWideGamut = 'w30r', /* little-endian RGB101010, 2 MSB are zero, wide-gamut (384-895) */
  kCVPixelFormatType_OneComponent16Half  = 'L00h',     /* 16 bit one component IEEE half-precision float, 16-bit little-endian samples */
  kCVPixelFormatType_OneComponent32Float = 'L00f',     /* 32 bit one component IEEE float, 32-bit little-endian samples */
  kCVPixelFormatType_TwoComponent16Half  = '2C0h',     /* 16 bit two component IEEE half-precision float, 16-bit little-endian samples */
  kCVPixelFormatType_TwoComponent32Float = '2C0f',     /* 32 bit two component IEEE float, 32-bit little-endian samples */
  kCVPixelFormatType_64RGBAHalf          = 'RGhA',     /* 64 bit RGBA IEEE half-precision float, 16-bit little-endian samples */
  kCVPixelFormatType_128RGBAFloat        = 'RGfA',     /* 128 bit RGBA IEEE float, 32-bit little-endian samples */
  kCVPixelFormatType_14Bayer_GRBG        = 'grb4',     /* Bayer 14-bit Little-Endian, packed in 16-bits, ordered G R G R... alternating with B G B G... */
  kCVPixelFormatType_14Bayer_RGGB        = 'rgg4',     /* Bayer 14-bit Little-Endian, packed in 16-bits, ordered R G R G... alternating with G B G B... */
  kCVPixelFormatType_14Bayer_BGGR        = 'bgg4',     /* Bayer 14-bit Little-Endian, packed in 16-bits, ordered B G B G... alternating with G R G R... */
  kCVPixelFormatType_14Bayer_GBRG        = 'gbr4',     /* Bayer 14-bit Little-Endian, packed in 16-bits, ordered G B G B... alternating with R G R G... */
};

您可以在文件中找到此信息.

如果您对此缓冲区的内容有视觉上的兴趣,可以使用CGBitmapContextCreate函数将CVPixelBuffer格式转换为UIImage ,并将其传递给CVPixelBuffer的基址.

+ (UIImage *)imageFromSampleBuffer:(CMSampleBufferRef)sampleBuffer
{
    // from : https://developer.apple.com/library/ios/qa/qa1702/_index.html

    // Get a CMSampleBuffer's Core Video image buffer for the media data
    CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer);

    // Lock the base address of the pixel buffer
    CVPixelBufferLockBaseAddress(imageBuffer, 0);

    // Get the number of bytes per row for the pixel buffer
    void *baseAddress = CVPixelBufferGetBaseAddress(imageBuffer);

    // Get the number of bytes per row for the pixel buffer
    size_t bytesPerRow = CVPixelBufferGetBytesPerRow(imageBuffer);

    // Get the pixel buffer width and height
    size_t width = CVPixelBufferGetWidth(imageBuffer);
    size_t height = CVPixelBufferGetHeight(imageBuffer);

    // Create a device-dependent RGB color space
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();

    // Create a bitmap graphics context with the sample buffer data
    CGContextRef context = CGBitmapContextCreate(baseAddress, width, height, 8,
                                                 bytesPerRow, colorSpace, kCGBitmapByteOrder32Little | kCGImageAlphaPremultipliedFirst);

    // Create a Quartz image from the pixel data in the bitmap graphics context
    CGImageRef quartzImage = CGBitmapContextCreateImage(context);

    // Unlock the pixel buffer
    CVPixelBufferUnlockBaseAddress(imageBuffer,0);

    // Free up the context and color space
    CGContextRelease(context);
    CGColorSpaceRelease(colorSpace);

    // Create an image object from the Quartz image
    UIImage *image = [UIImage imageWithCGImage:quartzImage];

    // Release the Quartz image
    CGImageRelease(quartzImage);

    return (image);
}

您还可以查看CMSampleBuffer(CoreMedia框架),这是此类媒体的另一个内部存储.