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Technical Q&A QA1249

How can I find out what non-RGB pixel formats a codec supports?

Q: Is there a way for an application to query a codec and find out what non-RGB pixel formats it supports?

A: Codecs supporting non-RGB pixel formats should have a 'cpix' resource included in their public resource list containing the four character codes of their supported non-RGB pixel formats. This information can be retrieved by applications using GetComponentPublicResource.

Listing 1 demonstrates how an application can check to see if a specific non-RGB pixel format is supported by a codec.

Listing 1

Boolean DoesCodecSupportPixelFormat(Component inComponent,

                                    OSType    inFormat)

  Boolean   isSupported = false;

  OSTypePtr *hResource = NULL;

  long      thePixelFormatCount;

  int       i;

  OSErr     err;

  // NOTE: GetComponentPublicResource returns a Handle,

  // not a resource - the caller should dispose this using

  // DisposeHandle

  err = GetComponentPublicResource(inComponent,

                                   'cpix', 1,

                                   (Handle*)&hResource);

  if (err || (NULL == hResource)) goto bail;

  thePixelFormatCount = GetHandleSize((Handle)hResource) / 4;

  for (i = 0; i &lt; thePixelFormatCount && !isSupported; i++)

    isSupported = ((*hResource)[i] == inFormat);

  DisposeHandle((Handle)hResource);

bail:

  return isSupported;

Codec Developers

A codec advertising support for '2vuy', 'r408' and 'v408' would for example, include a 'cpix' resource as part of their public resource list which looks like Listing 2.

Listing 2

resource 'cpix' (kMyCPIXResID) {

     '2vuy','r408','v408'

};

Document Revision History

Date	Notes
2008-04-24	Editorial
2004-01-05	New document that applications can find out if a codec supports non-RGB pixel formats.