Inside Macintosh: QuickTime Components
Apple has defined a component type value for sequence grabber channel components--that type value is 'sgch' . You can use the following constant to specify this type value:
#define SeqGrabChannelType 'sgch';
Sequence grabber channel components use their component subtype value to indicate the media type created by the component. For example, a channel component that works with video data would have a subtype of 'vide' (this value is defined by the Movie Toolbox's VideoMediaType constant).