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Q: Does the Sequence Grabber add clean aperture and aspect ratio information on behalf of a Video Digitizer?A: The Sequence Grabber will always automatically generate Clean, Production and Encoded dimensions for a captured video track based on the Clean Aperture ( In some versions of QuickTime since 7.1, when a Video Digitizer does not return Clean Aperture and Pixel Aspect Ratio information the Sequence Grabber will automatically generated Clean, Production and Encoded dimensions based on the codec type (this is fine when compressing to DV or DVCPRO50 for example). However, specifically in the case of uncompressed video (where this information cannot be determined based only on codec type) the generated Clean, Production and Encoded dimensions assume the Pixel Aspect Ratio is 1:1. This assumption may not be correct and can lead to unexpected capture results. In future versions of QuickTime, the Sequence Grabber will only generate the Clean, Production and Encoded dimensions when a Video Digitizer specifically returns Clean Aperture and Pixel Aspect Ratio Image Description extensions. If the How should I update my Video Digitizer?To ensure consistent behavior for all versions of QuickTime, Video Digitizer developers are encouraged to return Clean Aperture and Pixel Aspect Ratio information as part of the Image Description returned by the IMPORTANT: Developers should consult QuickTime Ice Floe 19 for a full discussion of Image Descriptions and required extensions. Listing 1: Adding pascal VideoDigitizerError MyVDig_GetImageDescription(MyVDigGlobals* glob,
ImageDescriptionHandle description)
{
SInt8 savedHState;
VideoDigitizerError err = noErr;
if (0 == description) return qtParamErr;
savedHState= HGetState((Handle)description);
if (err = MemError()) return err;
err = HUnlock((Handle)description);
if (err = MemError()) return err;
err = SetHandleSize((Handle)description, sizeof(ImageDescription));
if (err = MemError()) return err;
...
// Set up the parts of the ImageDescription that don't vary by input standard or input format
(**description).idSize = sizeof(ImageDescription);
(**description).resvd1 = 0;
(**description).resvd2 = 0;
(**description).dataRefIndex = 0;
(**description).vendor = kMyVDIGManufacturer;
(**description).temporalQuality = 0;
(**description).spatialQuality = codecMaxQuality;
// See note below
(**description).width = glob->myDigitizerRect.right - glob-> myDigitizerRect.left;
(**description).height = glob-> myDigitizerRect.bottom - glob-> myDigitizerRect.top;
(**description).hRes = 72 << 16;
(**description).vRes = 72 << 16;
(**description).frameCount = 1;
(**description).depth = 24;
(**description).clutID = -1;
// Add the ImageDescription properties that don't vary by input standard or input format
// NOTE: In all cases except DVCPROHD, the Image Description width and height
// are the Encoded Dimensions. Setting the height and width properties below negates
// having to directly set them in the Image Description above.
// Doing both may be redundant, although safe.
// Encoded width property
/*
* The width of the encoded image. Usually, but not always, this is
* the ImageDescription's width field.
*/
SInt32 width = (**description).width;
err = ICMImageDescriptionSetProperty(description, kQTPropertyClass_ImageDescription,
kICMImageDescriptionPropertyID_EncodedWidth, sizeof(SInt32),
&width);
if (noErr != err) goto bail;
// Encoded height property
/*
* The height of the encoded image. Usually, but not always, this is
* the ImageDescription's height field.
*/
SInt32 height = (**description).height;
err = ICMImageDescriptionSetProperty(description, kQTPropertyClass_ImageDescription,
kICMImageDescriptionPropertyID_EncodedHeight, sizeof(SInt32),
&height);
if (noErr != err) goto bail;
// The remaining portions of the Image Description that may vary based on input standard or format
CleanApertureImageDescriptionExtension cleanAperture;
PixelAspectRatioImageDescriptionExtension pixelAspectRatio;
if (ntscReallyIn == glob->myInputStandard) {
// Setup properties for NTSC 525-line video signals sampled at 13.5 MHz
// NOTE: these values will vary depending on your specific format - consult Ice Floe 19
// http://developer.apple.com/quicktime/icefloe/dispatch019.html#clap
cleanAperture.cleanApertureWidthN = 704; // (640 * 11/10)
cleanAperture.cleanApertureWidthD = 1;
cleanAperture.cleanApertureHeightN = 480;
cleanAperture.cleanApertureHeightD = 1;
cleanAperture.horizOffN = 0;
cleanAperture.horizOffD = 1;
cleanAperture.vertOffN = 0;
cleanAperture.vertOffD = 1;
// http://developer.apple.com/quicktime/icefloe/dispatch019.html#pasp
if (glob->myFrameIs4by3) {
/* "Non-Square 525"
Digital 525 (SMPTE 125M-1995, 13.5 MHz)
525-line analog video sampled at 13.5 MHz
(e.g., composite NTSC)
*/
pixelAspectRatio.hSpacing = 10;
pixelAspectRatio.vSpacing = 11;
} else {
/* Digital 525 (SMPTE 267M-1995, 13.5 MHz)
525-line analog video sampled at 13.5 MHz
(e.g., composite NTSC)
720x483 progressive 16:9 (SMPTE 293M-1996, 13.5 MHz)
*/
pixelAspectRatio.hSpacing = 40;
pixelAspectRatio.vSpacing = 33;
}
// codec info
(**description).cType = kMyFormat;
(**description).version = glob->myVersion;
(**description).revisionLevel = glob->myRevisionLevel;
(**description).dataSize = kFormatBufferSize;
PLstrncpy((**description).name, glob->myFormatTypeName,
glob->myFormatTypeName[0] < 32 ? storage->myFormatTypeName[0] : 31);
// Add the Image Description properties
// Clean Aperture
/*
* Describes the clean aperture of the buffer.
*/
err = ICMImageDescriptionSetProperty(description, kQTPropertyClass_ImageDescription,
kICMImageDescriptionPropertyID_CleanAperture,
sizeof(CleanApertureImageDescriptionExtension),
&cleanAperture);
if (noErr != err) goto bail;
// Pixel Aspect Ratio
/*
* Describes the pixel aspect ratio.
*/
err = ICMImageDescriptionSetProperty(description, kQTPropertyClass_ImageDescription,
kICMImageDescriptionPropertyID_PixelAspectRatio,
sizeof(PixelAspectRatioImageDescriptionExtension),
&pixelAspectRatio);
if (noErr != err) goto bail;
...
}
...
bail:
HSetState((Handle)description, savedHState);
return err;
}
ReferencesDocument Revision History
Posted: 2008-11-20 |
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