QMedia v1.5

Using QMedia

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Requirements | How grabbing works | Grabber setup

How Grabbing Works

QMedia does not access or control grabbing hardware directly; rather, it uses the grabbing capabilities built into QuickTime. QuickTime is system-level software and has a component architecture. QuickTime also provides the hardware abstraction layer that enables communication with a variety of hardware devices.

QMedia delegates most of the work involved to QuickTime’s Sequence Grabber. The Sequence Grabber allows applications to obtain digitized data from external sources such as video capture boards. The Sequence Grabber is responsible for orchestrating the entire operation: it collects digitized data from external sources and displays or saves the data in movie files (or both). The Sequence Grabber is represented in QMedia by a plug-in area.

The Sequence Grabber communicates with lower-level components called Grabber Channels. Grabber Channels are responsible for receiving digitized media from different sources at the same time. For example, an application could capture both video and sound from a VCR, or capture video from a VCR and sound from an external microphone. QMedia includes commands for creating, configuring and destroying channels in the grabber plug-in area.

The Grabber Channel components communicate with even lower-lever components called Digitizers. Digitizers talk to video and sound boards, digitize incoming data, and feed these data into the channels. There exist video digitizers (vdig) that handle video, whereas sound digitizers (sdig) handle sound. Digitizers are usually made by the board manufacturer.