## MMPM/2 Device Driver Reference

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### Capture

Video images can be captured one frame at a time when directed by the application. This type of capture mode is referred to as asymmetric capture because the time between successive frames is not constant. The frame rate is determined by the length of time that the application delays between taking image snapshots. Asymmetric capture is performed with IOCtls only; the MMPM/2 streaming mechanism is not used.

Typically, a stream is established to read a series of moving images from the device. This continuous capture mode is called symmetric or real-time capture, and is done at a constant frame rate and constant frame size. When established, a stream captures images continuously without assistance from the application code. A running stream cannot dynamically alter frame rate or size; but video quality attributes such as brightness, hue, and contrast can be altered dynamically. The command used in streaming capture can be found in the Device Driver Commands (DDCMD) messages and Stream-Handler Device (SHD) messages sections.

Streaming capture is used to make real-time movies and to monitor live video on frame-grabber cards.