Technical Q&A QA1501

Core Video - Available Pixel Formats

Q: What pixel formats does Core Video currently support, and is there an API that can be used to retrieve this information programatically?

A: A Core Video Pixel Buffer (represented by the opaque type CVPixelBufferRef) is an image buffer that holds pixels in main memory. Applications generating frames, compressing / decompressing video or using Core Image can all make use of Core Video Pixel Buffers.

Individual pixel buffers can be created and managed using APIs such as CVPixelBufferCreate, CVPixelBufferCreateWithBytes, CVPixelBufferGetWidth, CVPixelBufferGetHeight and so on (see CVPixelBuffer.h). A pool of pixel buffers can also be created for managing a set of CVPixelBuffer objects that are going to be recycled, for example, during a compression operation (see CVPixelBufferPool.h) and CIImage objects can be created from pixel buffers using methods such as initWithCVImageBuffer:.

At the time of this writing (Mac OS X 10.4.8 w/QuickTime 7.1.3), Core Video supports the pixel formats shown in Table 1. Note that new pixel formats may be added over time:

Table 1: Core Video supported pixel formats.

There are two APIs that can be used to dynamically retrieve all the pixel format OSTypes and Pixel Format Descriptions known to Core Video:

Use CVPixelFormatDescriptionArrayCreateWithAllPixelFormatTypes to retrieve an array of OSTypes.

CFArrayRef CVPixelFormatDescriptionArrayCreateWithAllPixelFormatTypes(CFAllocatorRef allocator)

Description:
    Returns a CFArrayRef containing a list of all supported pixel format types.

allocator - The allocator used to allocate memory for the array and its storage for values.
            Pass kCFAllocatorDefault to specify the default allocator.

Use CVPixelFormatDescriptionCreateWithPixelFormatType to retrieve a pixel format description dictionary.

CFDictionaryRef CVPixelFormatDescriptionCreateWithPixelFormatType(CFAllocatorRef allocator,
                                                                  OSType pixelFormat)

Description:
    Returns a CFDictionaryRef containing the pixel format description for the passed in pixel format type.

allocator - The allocator to use when creating the description. Pass kCFAllocatorDefault to specify the
            default allocator.

pixelFormat - A four-character code that identifies the pixel format description you want to obtain.

Notes:
    The returned Core Foundation dictionary contains the pixel format description. See “Pixel Format
    Description Keys” for more detailed information regarding the keys relevant to the format description.

Pixel Format Description Dictionary Keys:

kCVPixelFormatName - The name of the pixel format (type CFString).

kCVPixelFormatConstant - The pixel format constant for QuickTime.

kCVPixelFormatCodecType - The codec type (type CFString). For example, '2vuy' or k422YpCbCr8CodecType.

kCVPixelFormatFourCC - The Microsoft FourCC equivalent code for this pixel format (type CFString).

kCVPixelFormatPlanes - The number of image planes associated with this format (type CFNumber).

kCVPixelFormatBlockWidth - The width, in pixels, of the smallest byte-addressable group of pixels
                           (type CFNumber). Assumed to be 1 if this key is not present.

kCVPixelFormatBlockHeight - The height, in pixels, of the smallest byte-addressable group of pixels
                            (type CFNumber). Assumed to be 1 if this key is not present.

kCVPixelFormatBitsPerBlock - The number of bits per block (type CFNumber). For simple pixel formats,
                             this value is the same as the traditional bits-per-pixel value. This key is
                             mandatory in pixel format descriptions.

kCVPixelFormatBlockHorizontalAlignment  - The horizontal alignment requirements of this format
                                          (type CFNumber). Assumed to be 1 if this key is not present.

kCVPixelFormatBlockVerticalAlignment - The vertical alignment requirements of this format (type CFNumber).
                                       Assumed to be 1 if this key is not present.

kCVPixelFormatHorizontalSubsampling - Horizontal subsampling information for this plane
                                      (type CFNumber). Assumed to be 1 if this key is not present.

kCVPixelFormatVerticalSubsampling - Vertical subsampling information for this plane
                                    (type CFNumber). Assumed to be 1 if this key is not present.

kCVPixelFormatOpenGLFormat - The OpenGL format used to describe this image plane (if applicable)
                             (type CFNumber). See the OpenGL specification for possible values.

kCVPixelFormatOpenGLType - The OpenGL type to describe this image plane (if applicable)
                           (type CFNumber). See the OpenGL specification for possible values.

kCVPixelFormatOpenGLInternalFormat - The OpenGL internal format for this pixel format (if applicable).
                                     (type CFNumber). See the OpenGL specification for possible values.

kCVPixelFormatCGBitmapInfo - The Core Graphics bitmap information for this pixel format (if applicable).

kCVPixelFormatQDCompatibility - Indicates whether this format is compatible with QuickDraw (type CFBoolean).

kCVPixelFormatCGBitmapContextCompatibility - Indicates whether this format is compatible with Core Graphics
                                             bitmap contexts(type CFBoolean).

kCVPixelFormatCGImageCompatibility - Indicates whether this format is compatible with the CGImage type
                                     (type CFBoolean).

kCVPixelFormatOpenGLCompatibility - Indicates whether this format is compatible with OpenGL (type CFBoolean).

kCVPixelFormatFillExtendedPixelsCallback - Specifies a custom extended pixel fill algorithm (type CFData).

Listing 1 demonstrates how to retrieve a list of supported Core Video pixel format types with the output produced shown in Listing 2.

Listing 1: Retrieving pixel format types known to Core Video.

{
    CFArrayRef pixelFormatDescriptionsArray = NULL;
    CFIndex i;

    pixelFormatDescriptionsArray =
    CVPixelFormatDescriptionArrayCreateWithAllPixelFormatTypes(kCFAllocatorDefault);

    printf("Core Video Supported Pixel Format Types:\n\n");

    for (i = 0; i < CFArrayGetCount(pixelFormatDescriptionsArray); i++) {
        CFStringRef pixelFormat = NULL;

        CFNumberRef pixelFormatFourCC = (CFNumberRef)CFArrayGetValueAtIndex(pixelFormatDescriptionsArray, i);

        if (pixelFormatFourCC != NULL) {
            UInt32 value;

            CFNumberGetValue(pixelFormatFourCC, kCFNumberSInt32Type, &value);

            if (value <= 0x28) {
                pixelFormat = CFStringCreateWithFormat(kCFAllocatorDefault, NULL,
                              CFSTR("Core Video Pixel Format Type: %d\n"), value);
            } else {
                pixelFormat = CFStringCreateWithFormat(kCFAllocatorDefault, NULL,
                              CFSTR("Core Video Pixel Format Type (FourCC):
                              %c%c%c%c\n"), (char)(value >> 24), (char)(value >> 16),
                              (char)(value >> 8), (char)value);
            }

            CFShow(pixelFormat);
            CFRelease(pixelFormat);
        }
    }
}

Listing 2: Output produced by Listing 1.

Core Video Pixel Format Type: 32
Core Video Pixel Format Type: 24
Core Video Pixel Format Type: 16
Core Video Pixel Format Type (FourCC): 2vuy
Core Video Pixel Format Type (FourCC): yuvs
Core Video Pixel Format Type (FourCC): r408
Core Video Pixel Format Type (FourCC): v408
Core Video Pixel Format Type (FourCC): BGRA
Core Video Pixel Format Type (FourCC): b64a
Core Video Pixel Format Type (FourCC): b48r
Core Video Pixel Format Type (FourCC): b32a
Core Video Pixel Format Type (FourCC): b16g
Core Video Pixel Format Type (FourCC): v308
Core Video Pixel Format Type (FourCC): v216
Core Video Pixel Format Type (FourCC): v210
Core Video Pixel Format Type (FourCC): v410
Core Video Pixel Format Type (FourCC): r4fl

Listing 3 shows an example of the Pixel Format Description dictionary values returned by calling CVPixelFormatDescriptionCreateWithPixelFormatType for k32ARGBPixelFormat and Listing 4 shows the Pixel Format Description values returned for k422YpCbCr8PixelFormat.

Listing 3: Pixel Format Description values for k32ARGBPixelFormat.

kCVPixelFormatConstant - 32
kCVPixelFormatBitsPerBlock - 32
kCVPixelFormatQDCompatibility - true
kCVPixelFormatCGBitmapContextCompatibility - true
kCVPixelFormatCGImageCompatibility - true
kCVPixelFormatCGBitmapInfo - kCGImageAlphaFirst | kCGBitmapByteOrder32Big
kCVPixelFormatFillExtendedPixelsCallback - Extended fill procedure for this pixel format

Mac OS X:
    kCVPixelFormatOpenGLFormat - GL_BGRA
    kCVPixelFormatOpenGLInternalFormat - GL_RGBA8

    PPC Based Mac (Big Endian):
        kCVPixelFormatOpenGLCompatibility - true
        kCVPixelFormatOpenGLType - GL_UNSIGNED_INT_8_8_8_8_REV

    Intel Based Mac (Little Endian):
        kCVPixelFormatOpenGLType - GL_UNSIGNED_INT_8_8_8_8

Listing 4: Pixel Format Description values for k422YpCbCr8PixelFormat.

kCVPixelFormatConstant - k422YpCbCr8PixelFormat
kCVPixelFormatBlockWidth - 2
kCVPixelFormatBitsPerBlock - 32
kCVPixelFormatFillExtendedPixelsCallback - Extended fill procedure for this pixel format

Mac OS X:
    kCVPixelFormatOpenGLCompatibility - true
    kCVPixelFormatOpenGLFormat - GL_YCBCR_422_APPLE
    kCVPixelFormatOpenGLInternalFormat - GL_RGB

    PPC Based Mac (Big Endian):
        kCVPixelFormatOpenGLType - GL_UNSIGNED_SHORT_8_8_REV_APPLE

    Intel Based Mac (Little Endian):
        kCVPixelFormatOpenGLType - GL_UNSIGNED_SHORT_8_8_APPLE

Windows (if Direct3D supports the format):
    kCVPixelFormatDirect3DCompatibility - true
    kCVPixelFormatDirect3DFormat - D3DFMT_UYVY
    kCVPixelFormatDirect3DType - D3DFMT_UYVY
    kCVPixelFormatDirect3DInternalFormat - D3DFMT_UYVY

References

• QuickTime Pixel Format FourCCs

• Pixel Format Description Keys

• Core Video Programming Guide

• Core Video Reference

• Technical Q&A QA1443, 'Using QTPixelBufferContextCreate with NewMovieFromProperties'

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Document Revision History

Posted: 2007-01-23