Media Control Interface

The Media Control Interface, MCI in short, is an aging high-level API developed by Microsoft and IBM for controlling multimedia peripherals connected to a Microsoft Windows or OS/2 computer, such as CD-ROM players and audio controllers.

MCI makes it very simple to write a program which can play a wide variety of media files and even to record sound by just passing commands as strings. It uses relations described in Windows registries or in the [MCI] section of the file SYSTEM.INI. One advantage of this API is that MCI commands can be transmitted both from the programming language and from the scripting language (open script, lingo aso). Example of such commands are mciSendCommand or mciSendString.

For a number of years, the MCI interface has been phased out in favor of the DirectX APIs.

MCI Devices

The Media Control Interface consists of 4 parts:

• AVIVideo
• CDAudio
• Sequencer
• WaveAudio

Each of these so-called MCI devices(eg.CD rom or vcd player) can play a certain type of files e.g. AVIVideo plays avi files, CDAudio plays cd tracks among others. Other MCI devices have also been made available over time.

Playing media through the MCI interface

To play a type of media, it needs to be initialized correctly using MCI commands. These commands are subdivided into categories:

• System Commands

The Windows API provides two methods for controlling the multimedia capabilities of the system. The first is a series of low-level functions. The second is the Windows Media Control Interface (MCI). The media control interface provides a high-level, device-independent interface for controlling multimedia devices on the system and is the recommended method for controlling multimedia devices in Windows.

There are two methods for issuing MCI commands: command messages and command strings. Command messages are sent by filling a memory structure (GROUP) and passing it to the MCI system. Command strings are English-like strings that are sent to the MCI system and parsed to determine the action to be taken. Command strings provide the same functionality as command messages with a simpler format. This tip examines how to use the media control interface using MCI command strings.

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Using MCI, a program has the ability to play and record (as appropriate) on any supported multimedia device. This includes the usual multimedia devices (wave audio, MIDI sequencer, CD audio) as well as some more unusual devices (VCR, videodisc, digital audio tape). The configuration information for MCI is stored in the WIN.INI and SYSTEM.INI files. The [mci] section of SYSTEM.INI maps the system device names to the device drivers controlling those devices. The [mci extensions] section of WIN.INI maps file extensions to the appropriate multimedia device.

The MCI configuration information for my system is shown below. There are five multimedia devices registered on the system: CD audio, MIDI sequencer, wave audio, AVI video and MPEG video.

[mci] cdaudio=mcicda.drv sequencer=mciseq.drv waveaudio=mciwave.drv avivideo=mciavi.drv MPEGVideo=mciqtz.drvThis configuration method makes MCI extensible. New multimedia devices with the proper drivers can be integrated with the MCI system even though the devices weren't invented when MCI was designed. The system can also use multiple devices of the same type by configuring them correctly in SYSTEM.INI. I recently completed a project using a “CD jukebox” - a five-platter CD-ROM unit. After modifying the MCI configuration information, I was able to address each of the CD-ROM platters as an independent device.

The MCI system commands are divided into four categories: system, required, basic and extended commands. The commands are described below along with some commonly used options.

MCI System Commands System commands are handled by the MCI system instead of by an MCI device. These commands provides provide system-level information. The system commands are break and sysinfo.

Command Description break Set up key to break MCI action sysinfo Gets MCI system information sysinfo all quantity sysinfo all name [index] sysinfo cdaudio quantity

Required Commands Required commands must be implemented for every device. Each device must also support a defined set of options for each command. The required commands are capability, close, info, open and status.

Command Description capability Gets information about device capabilities capability cdaudio can eject close Closes an open device close all close cdaudio info Gets information about the device driver info cdaudio product open Opens and initializes a device open cdaudio open waveaudio!c:\win95\media\chimes.wav open c:\win95\media\chimes.wav type waveaudio open waveaudio!chimes.wav alias chimesound open sequencer!canada.mid open canada.mid type sequencer alias anthem status Gets device status status cdaudio mode status sequencer mode

Basic Commands Basic commands are device control commands that are may or may not be implemented depending on the device. The commands that are implemented must support a standard set of options for that command. The basic commands are load, pause, play, record, resume, save, seek, set, status and stop.

Command Description load Loads a device file from disk pause Pauses playing or recording pause cdaudio pause anthem play Starts playing the device play cdaudio play cdaudio from 3 to 4 play waveaudio play chimesound record Starts recording data with the device record waveaudio resume Resumes playing or recording after pause resume cdaudio save Save a device file to disk save waveaudio c:\temp\newsound.wav seek Moves to a specified position for the device seek cdaudio to start seek cdaudio to 3 seek waveaudio to 1000 set Updates device control settings set cdaudio door open set cdaudio door closed set waveaudio time format milliseconds set cdaudio time format tmsf status Gets device status status cdaudio current track status anthem length status cdaudio length track 3 status cdaudio number of tracks status waveaudio time format stop Stops playing or recording stop cdaudio stop anthem

Extended Commands Extended commands are additional commands that may be implemented for a specific device or that extended that options on a required or basic command. Examples of extended commands are delete and spin. Delete is used to delete a section of a wave audio file. Spin is used to start or stop spinning on a videodisc device. These commands are implemented only for the devices they apply to.

The MCI Command String Functions Two API functions are involved when using MCI command strings: mciSendString and mciGetErrorString. The functions are prototyped and used in the Media Control Interface Tester sample program. This program allows the user to enter and execute an MCI command string. The program provides a way to test the result of various MCI command strings.

The program includes some sample MIDI files for testing. You can use these along with other multimedia files on your system to test some of the following command strings and see their results.

To test the wave audio device on your system, try:

open c:\win95\media\chimes.wav type waveaudio play c:\win95\media\chimes.wav close c:\win95\media\chimes.wav open c:\win95\media\chimes.wav type waveaudio alias chimes play chimes close chimes open waveaudio!c:\win95\media\chimes.wav alias chimes play chimes close chimesTo test the MIDI sequencer on your system, try:

open sequencer!canada.mid alias anthem play anthem pause anthem resume anthem stop anthem seek anthem to start play anthem stop anthem close anthemTo test the CD drive on your system, try:

open cdaudio play cdaudio set cdaudio time format tmsf play cdaudio from 3 to 4 close cdaudioIf you do much work with the MCI system, you will probably want to obtain a Windows API reference so that you have full documentation for the MCI command structure. For basic MCI work, you now have to tools needed to integrate the media control interface and its capabilities into your Clarion programs.

• Required Commands
• Basic Commands
• Extended Commands

A full list of MCI commands can be found at Microsoft's MSDN Library.

External links

• Microsoft MCI Reference - MSDN Library