## Presentation Device Driver Reference for OS/2

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### Software Motion Video Support

The software motion video component of the Multimedia Presentation Manager/ 2 must update bit maps very quickly. The system must be able to play movie files at 15 frames per second or faster, with each frame having a bit map size of 320 x 240 pels or larger.

GPI calls such as GpiBitBlt cannot meet these objectives. A set of DevEscape calls are provided so that the software motion video component can directly update the Video Random Access Memory (VRAM) of packed-pel display adapters.

Most of the movie frames are delta frames, containing only those pels that have changed from the previously displayed frame. By directly updating VRAM , the software motion video component only needs to selectively update a small number of pels in a typical 320 x 240 pel image. This selective updating allows better performance than a GPI call, which requires redrawing of the entire bit map and makes a heavy call/return overhead when updating small runs of pels.

Software motion video DevEscape functions are provided to:

Query the attributes of the aperture (DEVESC_GETAPERTURE)

Switch the bank address (DEVESC_SWITCHBANK)

Reserve a video adapter (DEVESC_ACQUIREFB)

Release a video adapter (DEVESC_DEACQUIREFB)