VFW v1.1 DK "ICM_DRAW_START_PLAY" Message (115763)

SUMMARY

The ICM_DRAW_START_PLAY and ICM_DRAW_STOP_PLAY messages are not documented in the "Programmer's Guide" included in the "Video for Windows Development Kit, version 1.1" (VFW 1.1 DK).

This article describes these messages in detail for the purpose of assisting a developer in writing a render driver.

MORE INFORMATION

The Installable Compression Manager (ICM) communicates with a renderer (also known as a render driver) by sending messages to it. The renderer interprets the message and responds accordingly.

The ICM_DRAW_START_PLAY message is sent either by the ICM or by an application that calls the ICDrawStartPlay() command. This message is sent to tell the driver the actual starting and ending times of a play operation. This message is sent to the driver before any frame data is sent.

ICM_DRAW_START_PLAY is sent with two DWORD parameters, dwParam1 (the starting time) and dwParam2 (the ending time). These times are typically interpreted as frame numbers.

If the ending time is less than the starting time (dwParam2 < dwParam1), then the segment plays backward.

The ICM_DRAW_STOP_PLAY message is sent when the ICDrawStopPlay() command is issued to indicate a play operation is over. dwParam1 and dwParam2 are not used with this message and should be ignored by the driver.