Working (and Playing!) with REXX and OS/2 Multimedia

By Timothy F. Sipples

This are the notes of a presentation gave by Timothy F. Sipples on 15 May 1994 at the Fifth Annual REXX Symposium.

What is Multimedia?

• Combining still images (bitmaps), animation, software motion video, text, and/or audio to present information
• Principle technologies: CD-ROM, laserdisc, digital audio, MIDI, high resolution displays with more colors
• Principle file formats: WAV, MID, and AVI
• Multimedia NOT invented by Comptons

...We like to call it ULTIMEDIA

Why use Multimedia?

• "It's the market, stupid."
• Triggers: to "describe" events
• Education/training
• Kiosks (point-of-sale)
• Presentations and demos
• Better human interfaces generally
• Entertainment and games

Requirements for OS/2 Multimedia

• OS/2 2.1 with Multimedia Presentation Manager/2 (included)
• Standard OS/2 hardware requirements
• Some additional RAM (to 12 MB) recommended
• CD-ROM drive
• Audio adapter (Creative Labs, MediaVision, IBM, etc.)
• Display with at least 256 colors recommended
• Video capture adapter (optional)
• Laserdisc player with computer control (optional)

Major Features in MMPM/2 1.1

• Multimedia folder
• Sound setup object (for system sounds)
• Applets
• Volume control
• Drivers
• Sample files
• Lotus 1-2-3 and Excel audio macros
• External function library for REXX and help file

Principle File Formats

• Generally a superset of Windows file formats
• WAV: Digital audio (pulse code modulation, and variants)
• MID: Standard MIDI file format (for instrumental music)
• AVI: Audio-video interleaved (IBM Ultimotion and Intel Indeo)
• Conversion applet for some additional file formats included (AVC, VOC, DIB, DMP, ADPCM, M-Motion)
• High degree of modularity permits addition of more file formats (e.g. FLI/FLC)

Principle REXX Features

• Multimedia with REXX help file
• PLAY.CMD
• RECORD.CMD
• Entire MCI (media control interface) command set available, not just subset described in online help
• External function library (MCIAPI.DLL) provides access to MCI command set

Key Limitations

• REXX is unable to deal with loss of device (meaning ACQUIRE EXCLUSIVE must be used)
• REXX program should not hold device exclusive for long
• Unless using PMREXX (or one of the visual REXX builders), MCI commands which require Presentation Manager (such as Ultimotion playback) will fail
• REXX does not receive PM messages (to easily monitor the status of playback and devices)
• MCI's implicit opens are assumed shareable (and not necessarily desired with REXX)

Sample REXX Script

/* Load and initialize Multimedia REXX support */
call RXFUNCADD 'mciRxInit','MCIAPI','mciRxInit'
call mciRxInit 

/* Open default digital audio device, exclusive use */
rc = mciRxSendString('open waveaudio alias wave wait','RetStr','0','0') 

/* Check error, call function to return error string */
if rc <> 0 then
do
	MacRC = mciRxGetErrorString(rc,'ErrStVar')
	say 'rc =' rc ', ErrStVar =' ErrStVar
end

/* Load a digital audio file */
rc = mciRxSendString('load wave sample.wav wait','RetStr','0','0') 

/* Obtain ID for device context that was just opened */
DevID = mciRxGetDeviceID(wave) 

say 'DevID =' DevID

/* Set the time format to milliseconds */
call mciRxSendString 'set wave time format ms','RetStr','0','0'

/* Determine whether the microphone connection enable */
call mciRxSendString 'connector wave query type microphone wait','RetStr','0','0'

say 'connector query microphone:  RetStr =' RetStr

/* Query length of the opened file, value in ms */
call mciRxSendString 'status wave length wait','RetStr','0','0'

say 'status wave length:  RetStr =' RetStr

/* Play the multimedia file, wait for completion */
call mciRxSendString 'play wave wait','RetStr','0','0'

/* "Rewind" to the beginning of the file */
call mciRxSendString 'seek wave to start wait','RetStr','0','0' 

/* Close the device context */
call mciRxSendString 'close wave','RetStr','0','0'

/* Ensure proper termination of Multimedia REXX */
call mciRxExit

exit(0)

Live Demos

• PLAY.CMD
• FOR..DO
• Ultimotion
• RECORD.CMD
• Modifications to the sample .CMD files
• Dial 1.1 by Helge Hafting

Links

• Additional info about the event