Types of Multimedia Device Drivers

As used in this documentation, the term audio device refers to MIDI, waveform, mixer, and auxiliary devices. Audio-compression drivers and video-compression drivers support these devices. Audio-compression drivers compress and decompress audio sequences. This section includes certain information about the Audio Compression Manager (ACM) as it applies to certain audio devices.

The term video device refers to devices that process and play video images. Video-compression drivers compress and decompress both still and motion video sequences. These drivers can support hardware-assisted and software-only compression and decompression.

The Windows multimedia services support the following types of multimedia devices and drivers:

• Auxiliary audio devices - to support audio data that gets mixed MIDI and waveform audio in a multimedia computer.
• Waveform input devices - to convert analog audio signals into digital information.
• Waveform output devices - to convert digital audio information into analog audio signals.
• MIDI input ports - to receive MIDI information from external MIDI devices like keyboards and drum machines.
• MIDI output ports - to send MIDI information to external MIDI devices.
• Internal MIDI synthesizers - to synthesize music from MIDI information sent by applications.
• Mixer devices - to control multiple audio lines.
• Video-capture devices - to digitize still images and motion video images. Some video-capture devices can also overlay and play video images.
• Audio compression and decompression drivers - to support a variety of audio data formats and files for playback and recording.
• Video compression and decompression drivers, and video draw drivers - to support a variety of video formats and files for displaying and creating.

Internal MIDI synthesizer devices and MIDI output ports are both MIDI output devices. They use the same entry-point function and receive the same messages.

The approach to writing drivers for each of the various types of audio devices is the same. Each type of driver requires a different entry-point function, but the structure of these functions is identical. They all have similar messages to process, although some types have unique messages for operations exclusive to that particular type of device.