Technical Q&A

QTMTB55 - SGSetSettings unexpected results (11-October-1999)

Q: I'm calling the QuickTime SGSetSettings function to configure the sequence grabber and its channels. The problem is, after I call this function once, subsequent calls to the function always return an error code, and the settings dialog box no longer appears. What's going on?

A: When you call the SGSetSettings function (described in Inside Macintosh: QuickTime Components, page 5-50) the sequence grabber will dispose of any of its current channels before applying this configuration information. It then opens connections to new channels as appropriate.

What this means is if you've created sequence grabber channels yourself (for example, with the SGNewChannel function) prior to calling SGSetSettings, the old references to these channels are no longer valid, and you must query the sequence grabber using the SGGetIndChannel function (described in Inside Macintosh: QuickTime Components, page 5-33) to re-acquire the channel references.