## MMPM/2 Device Driver Reference

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### PDD Sample for MPEG Video Playback Devices

The Developer Connection Device Driver Source Kit for OS/2 provides a sample MPEG Video Playback physical device driver (PDD) to assist in the creation of PDDs for other video playback devices. This sample provides a code base for a new PDD, simplifies development, and illustrates the OS/2 MPEG Video Playback PDD model for a nonshared frame buffer device, also referred to as an overlay device. The ReelMagic card from Sigma Designs, Inc. is an example of such a device.

The code contained in this sample was derived from a working driver. All hardware-specific code and header files have been removed from the sample. Although this device driver was written for a device that uses the split- stream model, it is easily adaptable to the single-stream model.

The split-stream MPEG I/O procedure splits the audio and video packets out of the MPEG file. The audio data packets are passed through the subsystem to the audio DD, and the video data packets are passed through the subsystem to the video DD. As the audio DD returns the buffers that it has played, it also returns the current audio time-which is in turn passed through the subsystem to MPEG hardware compressor/decompressor (CODEC) and from there is sent to the video DD on the next VCAI_PLAY command.

The single-stream MPEG I/O procedure reads the entire MPEG file one buffer at a time-without splitting the video and audio data. As each buffer is read in, it is passed through the subsystem to the video DD. With single stream, every byte in the file is passed to the DD; whereas with split stream, only the video data packets are passed to the video DD. The single- stream video DD and its hardware are then responsible for producing the video and audio along with all synchronization.

Note: From the video DD's perspective, the main difference in the single- stream model is that the SCR, PTS, and Audio PTS fields in the VCAI_PLAY contain zero.