Multimedia: The Basics

Article
02/20/2014

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This chapter describes the multimedia architecture and features in Windows 95.

For users of multimedia applications and equipment in your organization, installing Windows 95 provides an immediate multimedia upgrade. Its standard architecture for digital video, digital audio, MIDI, and file handling allow for high-quality multimedia effects. This architecture provides the following benefits:

You can use the Media Control Interface (MCI) to run multimedia devices independently from each other.
You have enhanced video support using the new Display Control Interface (DCI). For more information, see Chapter 19, "Devices."
You can use built-in programs to record, edit, and play digital audio and video.
You can easily add new multimedia hardware through the Add New Hardware option in Control Panel. The Add New Hardware option is a wizard that guides you through the steps to install and configure drivers for legacy devices. For more information, see Chapter 19, "Devices."
You can use the new built-in file sharing to share CD-ROM drives across the network. For more information, see Chapter 11, "Logon, Browsing, and Resource Sharing."

The performance benefits from the 32-bit Windows 95 architecture ensures that Windows 95 multimedia titles can include digital video and sound with better quality than ever before.

Multimedia: The Issues

In the corporate environment, you need to consider what multimedia features your users will be using to determine what extra hardware they'll need. For example, to use the audio capabilities as described in this chapter, computers need a sound card. For more information, see "Buying a Multimedia Computer" later in this chapter.

Windows 95 includes basic audio recording, audio playback, and video playback tools, but your users might need more features than these tools offer. For example, if users will be capturing and compressing digital video, they'll need additional software. Consider which additional multimedia software tools you might need to purchase. For more information, see "Buying a Multimedia Computer" later in this chapter.

If you are planning to play video clips over the network, playback will probably appear somewhat jerky unless your network guarantees a continuous data stream (for example, if you use an isochronous Ethernet network or an asynchronous transfer mode (ATM) network).

Multimedia Overview

This section describes the Windows 95 components that support multimedia hardware and software.

Media Control Interface

The Media Control Interface (MCI) provides applications created for Windows 95 with device-independent capabilities for controlling media devices such as audio hardware, videodisc players, and animation players. This interface works with MCI device drivers to interpret and run MCI commands such as pause, play, and stop.

MCI provides a set of core commands for a broad range of media devices. For example, MCI uses the same command to begin playback of a waveform-audio file, a videodisc track, and an animation sequence. MCI also provides extended commands for using particular device types with unique capabilities, such as using a frame-based time format for animation. For more information about MCI drivers and commands, see the Microsoft Windows 95 Device Development Kit.

A device type identifies a class of MCI devices that respond to a common set of commands. The following table lists the currently defined MCI device types.

Device type	Description
animation	Animation device
cdaudio	Compact disc (CD) audio player
dat	Digital audiotape player
digitalvideo	Digital video in a window (not GDI based)
other	Undefined MCI device
overlay	Overlay device (analog video in a window)
scanner	Image scanner
sequencer	MIDI sequencer
vcr	Videocassette recorder or player
videodisc	Videodisc player
waveaudio	Audio device that plays digitized waveform-audio files

Multimedia Files

Usually, multimedia files are maintained in one of the formats described in the following table.

Format	Corresponding filename extension
Digital-video	.AVI
Waveform-audio	.WAV
Musical Instrument Digital Interface (MIDI)	.MID

Multimedia files are stored on a compact disc, a local hard disk drive, a network file server, or another storage medium. The playback quality is constrained by the amount of data that the storage medium can continuously supply to the file system.

A multimedia data stream (such as an .AVI file) generally contains multiple components, such as digital-video data, audio data, text, and perhaps other data (such as hot-spot information, additional audio tracks, and so on). As multimedia information is read from the CD-ROM drive, the multimedia subsystem determines what the data stream contains, and then it separates and routes the data accordingly.

CD-ROM File System

To get the best possible performance from double-speed and faster CD-ROM drives, Windows 95 includes a new, 32-bit, CD-ROM file system (CDFS) for reading files from CD-ROM drives as quickly and efficiently as possible. For more information about the CDFS, see Chapter 17, "Performance Tuning" and Chapter 31, "Windows 95 Architecture."

CDFS replaces most Windows version 3.1 MSCDEX drivers.

Display Control Interface

The Display Control Interface (DCI) is a new display driver interface created jointly by Microsoft and Intel Corporation. DCI-compliant drivers provide a fast, direct way for games and digital video in Windows 95 to write to the video frame buffer. It also enables digital-video playback to take advantage of several specific kinds of hardware support included on advanced graphics adapters.

For more information about DCI, see the DCI Level 2 Specification. This specification is available through the Microsoft Developer Network (MSDN); to obtain it, call (800) 759-5474, or, from outside the United States and Canada, call (402) 691-0173. For more information about MSDN, see Appendix J, "Windows 95 Resource Directory"

Support for Multimedia Devices

Windows 95 includes built-in support for common multimedia authoring devices such as laser discs and video-cassette recorders (VCRs). This makes it easy to set up a computer for step capture, a process in which a user captures digital-video data one frame at a time; the data is usually compressed later. This is a slow process, but it is the best way to get the best possible quality of digital video.

To play the contents of a videotape on a computer, users must connect the video and audio outputs from the VCR to the video-capture or overlay and to the audio inputs of the computer. Users might also need to install an MCI digital-video device driver.

Recording, Editing, and Playing Audio

Windows 95 multimedia services provide extensible, device-independent audio support. Windows 95 features services for sound control for computers that have sound cards and for waveform-audio, MIDI, and mixer devices.

With audio support in Windows 95, users can do the following:

Use the Sound option in Control Panel to assign sound clips to play each time a specific event occurs
Use CD Player to play audio CDs
Use Sound Recorder to record sound
Use built-in Windows 95 OLE support to copy or link audio clips in other documents, as described in Chapter 22, "Application Support"

For more information about recording, editing, and playing multimedia files, see online Help.

Windows 95 Support for MIDI

Musical Instrument Digital Interface (MIDI) is a serial interface standard that allows for the connection of music synthesizers, musical instruments, and computers. The MIDI standard is based partly on hardware and partly on a description of the way in which music and sounds are encoded and communicated between MIDI devices.

MIDI is used as a development tool for musicians. Virtually all advanced music equipment supports MIDI, and MIDI offers a convenient way to control the equipment very precisely. MIDI is similar to the electronic equivalent of sheet music. For example, if you buy a CD that contains a particular performance of a piece of music, the data on the CD requires no interpretation at all — it's straightforward playback. If you buy the sheet music and have someone play it, it requires very little data, but, depending on the quality of the instruments and the musicians, you can get a good or bad interpreration of that piece of music.

Windows 95 supports the General MIDI Specification to request particular instruments and sounds. This specification is an industry standard that defines how MIDI should be used, and it is supported by Microsoft and most MIDI sound card manufacturers.

Windows 95 supports a new technology called MIDI streams. This technology is used in advanced sound cards to play very complex MIDI sequences with less CPU use. Support for this technology allows Windows 95 to communicate multiple MIDI instructions simultaneously within a single interrupt. As a result, playing MIDI files now requires even less computing power than it did before, and it allows developers to process MIDI instructions, graphics, and other data even more successfully.

For more information about playing a MIDI sound file, see online Help.

Recording Sound

Users who have microphones connected to their computer can record sound by using Sound Recorder.

When using Sound Recorder, users must use a real-mode compression codec. To turn on voice compression when recording so that the file is compressed in real-time, users must use the GSM 6.10 format in the Sound Selection dialog box in Sound properties.

For more information about recording sound with a microphone, see online Help.

Controlling Audio Input Levels

Windows 95 includes a Volume Control tool that provides audio line routing services to manage the different audio lines installed on a computer. An audio line consists of one or more channels of waveform-audio data coming from one origin or system resource. For example, a stereo audio line has two data channels, yet it is considered a single audio line. Each audio line also has zero or more mixer controls associated with it. A mixer control can take on a number of different characteristics (such as controlling volume) depending on the characteristics of the associated audio line.

The number of lines users can mix by using Volume Control depends on the number of audio source lines the computer has, and whether they are using Volume Control for input or output.

For more information about mixing sounds, see online Help.

Playing and Recording Digital Video

Windows 95 video services provide the resources for capturing video clips, compressing the content, and controlling playback.

Displaying digital video involves moving and processing huge streams of data continuously and efficiently. In earlier versions of Windows, the process of displaying digital video relied on a series of 16-bit systems — from reading data from the disk, to decompressing the video data, to displaying it on the screen. With the Windows 95 32-bit architecture, users can display bigger, smoother, and more colorful digital video than ever before, without adding any hardware.

Windows 95 multimedia is fully compatible with 16-bit multimedia titles. Early testing has shown that the 32-bit improvements in file access speed and stream handling result in performance gains for 16-bit multimedia applications and especially for the new generation of 32-bit applications developed for Windows 95.

To determine the format in which an existing video clip was authored

Right-click the icon for the digital-video file, click Properties, and then click the Details tab.

For more information about playing media clips, see online Help.

Buying a Multimedia Computer

The following list provides guidelines for what to look for in a multimedia system, plus specifics for overall sound components, MIDI components, mixing capabilities, and video components.

What to Look for in Basic Computing Power

Make sure to select a balanced computer, in which all components work together to meet the demands of supporting multimedia applications. In multimedia systems, balance is more important than speed, because multimedia playback places heavy demands on the CD-ROM (for reading data), on the hard disk (for writing data), on the CPU (for decompressing), and on the video and audio subsystems (for playback). A fast CPU alone does not guarantee a great playback system. For best results, the computer should have the following components:

Local-bus video. The performance of a computer with a local bus is about 10 times better than one without a local bus, assuming everything else on the computers is equal. Without local-bus video, a computer will not be able to keep up with the amount of video data that consumer multimedia applications and games currently being produced will attempt to display continuously. Preferably, the system should include a PCI bus.
A 24-bit display monitor. This is required for TrueColor support.
A double-speed or faster CD-ROM drive. New multimedia applications assume double-speed data rate.
Super VGA (800x600) resolution or better with 16-bit color. Because multimedia applications display many different colors and they tend to compete for access to the system palette, it's important to have support for more than 8-bit color.
16-bit audio and MIDI. Many multimedia applications make use of sound cards with MIDI support.

What to Look for in Computer Sound Support

The following are some key features to look for when you want to purchase a multimedia computer with great sound support:

Choose a sound card with a 16-bit digital-to-analog converter (DAC) for playback, and a 16-bit analog-to-digital converter (ADC) for recording (necessary for applications developers).
Look for a CD-ROM drive with double-speed or faster capabilities and multisession support.
Look for a system that supports stereo sound and 8, 11, 22, and 44 kilohertz (kHz) waveforms. Compact-disc quality sound uses 44 kHz. The 11 kHz and 22 kHz waveforms are fractions of 44 and are often used for compressed waveforms that are meant to save CPU processing. The 8 kHz waveform is used for Truespeech™ compression.
Developer systems should also include full-duplex support to record and play sound at the same time.

What to Look for in Computer MIDI Support

Microsoft recommends that sound cards for both consumer and developer systems include the following:

General MIDI support. General MIDI refers to a system of assigning numbers to each kind of instrument, so that, for example, instrument 12 on one computer is the same as instrument 12 on all others.
Polyphony, which means the ability to play multiple sounds at the same time. Consumer systems should include 16-voice polyphony; developer systems should include at least 20-voice polyphony. Support for more concurrent sounds means a fuller-sounding playback.
MIDI streams. This is an efficient, new capability in Windows 95 whereby a sound card receives and batch-processes multiple MIDI messages (such as Note On and Note Off). With MIDI-stream sound support in the sound subsystem, the CPU is freed from managing those messages individually. This offers virtually flawless playback, even when the CPU is being heavily taxed by large-frame video playback.
Sampled sound rather than waveform synthesis. Sampled sound is an actual recording of a sound. Waveform synthesis uses a mathematical approximation of that sound.
Standard MIDI port. Consumers and developers use this port to plug in MIDI devices, such as piano-style keyboards. It also supports joysticks.

What to Look for in Mixing Capabilities

A good multimedia system for either a user or a developer should have mixing capabilities. Look for the following features:

The mixer should mix input from four sources (WAV, MIDI, Redbook, AUX) and present the output as a stereo, line-level audio signal at the back panel of the computer. Each input should have at least a 3-bit volume control (8 steps) with a logarithmic taper.
Make sure that all sources are within – 10 dB and without attenuation. This will ensure that the mixer will not clip, meaning that if a sound peaks, the audio clicks instead of playing that sound. It also ensures that the mixer will output between 0 dB and +3 dB.
The preferred system should have individual audio source and master digital volume control registers and extra line-level audio sources.

What to Look for in Computer Video Support

The following are some key video-support features to look for when purchasing a multimedia computer:

Look for a balanced system in which each component has sufficient power. This is important because any of several components on the system could adversely affect the playback quality of a multimedia application. The computer might not have enough space on the CD-ROM or hard disk; the hard disk might not be able to retrieve data fast enough to play back well; the CPU might not have enough power to handle the decompression of the video; or the bus on the video display card might not be fast enough to move all of the data to the screen.
Look for Super VGA resolution. The minimum resolution for a multimedia computer is VGA, which provides a 640x480-pixel image and 256 colors, also expressed as 8 bits per pixel (bpp). Microsoft recommends that a consumer system include at least a Super VGA display, which provides 800x600-pixel resolution with approximately 64,000 colors (16 bpp) for users working with complicated graphics.

For example, suppose that you are playing a video segment with a shaded maroon background that includes one underwater scene, followed by a skydiving scene, followed by a city street scene. Each scene and its background has very different color qualities. At least one of the scenes or the background will not be displayed well if a full-color clip is translated to a 256-color display.
Look for a video card with a DCI provider for better performance.
Look for a computer with a double-speed or faster CD-ROM drive, which reads data from the CD-ROM at a rate of at least 300 kilobytes per second. This is the rate needed to have good-looking 320x240-pixel digital video clips playing at a reasonable frame rate with no undue screen compression. (Screen compression changes resolution, causing a grainy image. At extreme compression, for example, an image of a person might look instead like a bunch of blocks.)

Troubleshooting Multimedia Software

This section describes how to identify and resolve multimedia software problems.

Note: Before you attempt any troubleshooting, shut down and restart the computer to verify that the system functions correctly.

For information about troubleshooting related hardware problems, see Chapter 19, "Devices."

Correcting Problems with Playing .WAV Files

When a multimedia application is unable to play waveform-audio (.WAV) files, it is usually due to one or more of the following problems:

The sound card is not installed properly.
You are using Sound Recorder, and a waveform-audio driver is not installed.
You are using Media Player, and a waveform-audio MCI driver is not enabled.

The sound card is not installed properly.

Most sound cards come with MS-DOS – based programs for playing sounds or testing card configurations. Run these test programs; if the sound card does not work with these programs, then it will not work with Windows 95 sound support.

Make sure the sound card settings do not conflict with other hardware. Use the Add New Hardware icon in Control Panel to detect your hardware, which will determine if you have any hardware for which the appropriate driver is not yet installed. Verify port and IRQ settings.

Note: If the sound card can play MIDI files, the card is properly installed.

A waveform-audio driver is not installed.

If you are running Sound Recorder and there is no waveform-audio driver installed, you will receive an error message. In this case, make sure that the waveform-audio driver is listed in the Multimedia Devices list; you can see this list by clicking the Advanced tab in the Multimedia option in Control Panel. If the sound card is compatible with Sound Blaster™, try using the Sound Blaster driver provided with Windows 95. If you cannot find the correct driver for the sound card in the list, try using the Windows 3.1 driver for that card.

A waveform-audio MCI driver is not enabled.

If you are running Media Player and cannot play .WAV files, perform the following procedure to correct the problem.

To enable the waveform-audio MCI driver

In the Multimedia option in Control Panel, click the Advanced tab.
In the Multimedia Devices list, click the plus (+) sign next to Media Control Devices.

If Wave Audio Device (Media Control) does not appear in the list, the driver is not installed.
Click Wave Audio Device (Media Control), and then click the Properties button.
In the properties dialog box, click Use This Media Control Device.

Correcting Problems in Playing MIDI Files

When a multimedia application is unable to play MIDI files, it is commonly due to one or more of the following problems:

The sound card is not installed properly.
You are using Sound Recorder and a MIDI driver is not installed.
A MIDI MCI driver is not installed.
The .IDF file is invalid or corrupt.

The sound card is not installed properly.

Make sure that the sound card settings do not conflict with other hardware. Use the Add New Hardware option in Control Panel to detect your hardware, which will determine whether you have any hardware for which the appropriate driver is not yet installed. Verify port and IRQ settings.

Note: If the sound card can play .WAV files, the card is properly installed.

A MIDI driver is not installed.

If you are using Sound Recorder and cannot play a MIDI file, it might be because there is no MIDI driver installed. If the sound card is compatible with AdLib, try using the AdLib driver provided with Windows 95. If you don't find the correct driver for the sound card in the list, try using the Windows 3.1 driver for that card (however, the Windows 3.1 driver might not be compatible with Windows 95).

A MIDI MCI driver is not installed or enabled.

In Media Player, make sure that the option named MIDI Sequencer appears in the Device menu. If not, then the MIDI MCI driver is not installed or not enabled.

To verify that the MIDI MCI driver is enabled

In the Multimedia option in Control Panel, click the Advanced tab.
In the Multimedia Devices list, click the plus (+) sign next to Media Control Devices.

If MIDI Sequencer Device does not appear in the list, the driver is not installed. See the following procedure for instructions.
Click MIDI Sequencer Device (Media Control), and then click the Properties button.
In the properties dialog box, click Use This Media Control Device.

To install the MIDI MCI driver

In the Add New Hardware option in Control Panel, click No when prompted to have Windows 95 search for your hardware, and then click the Next button.
In the Hardware Types list, click Sound, Video And Game Controllers, and then click the Next button.
Click Microsoft MCI in the Manufacturers list, and then click MIDI Sequencer Device (Media Control) in the Models list. Click the Next button.
To complete the installation, click the Finish button.

The .IDF file is corrupt or invalid.

Copy the appropriate .IDF file for each device installed. For general MIDI devices, obtain a new copy of GENERAL.IDF from the Windows 95 disks. For MIDI devices that come with their own .IDF file, reinstall the file from the device's setup disks.

Correcting Problems with Playing or Hearing an Audio CD

When a user is unable to hear an audio CD being played, it is commonly due to one or more of the following problems:

The CD-ROM drive is not installed properly.
An MCI CD audio driver is not installed.
The CD-ROM drive and the sound card are not connected.

The CD-ROM drive is not properly installed.

Place a data CD in the CD-ROM drive and make sure you can view the files in Windows Explorer or list the files at the command prompt. If you can, then the CD-ROM drive is properly installed. If not, verify your disk drivers (ESDI, SCSI, Proprietary, MSCDEX) and make the appropriate configuration changes so that you can view the files on a data CD.

The CD audio MCI driver is not installed.

In Media Player, make sure that the option named CD Audio appears in the Device menu. If not, then the CD audio MCI driver is not installed or not enabled.

To verify the CD audio MCI driver is enabled

In the Multimedia option in Control Panel, click the Advanced tab.
In the Multimedia Devices list, click the plus (+) sign next to Media Control Devices.

If CD Audio Device (Media Control) does not appear in the list, the driver is not installed. See the following procedure for instructions.
Click CD Audio Device (Media Control), and then click the Properties button.
In the properties dialog box, click Use This Media Control Device.

To install the CD audio MCI driver

In the Add New Hardware option in Control Panel, click No when prompted to have Windows 95 search for your hardware, and then click the Next button.
In the Hardware Types list, click Sound, Video And Game Controllers, and then click the Next button.
Click Microsoft MCI in the Manufacturers list, and then click CD Audio Device (Media Control) in the Models list. Click the Next button.
To complete the installation, click the Finish button.

The CD-ROM is not connected to the sound card.

If the CD-ROM is playing and there is no sound coming from the sound card speakers, try plugging the speakers or headphones into the audio jack on the face of the CD-ROM drive. If you get sound, then check the internal or external audio connection between the CD-ROM drive and the sound card.

Correcting Problems with Hearing from Headphones

Verify that the sound card is correctly installed by reviewing the card's properties.

To view your sound card's properties

In the Multimedia option in Control Panel, click the CD Music tab.
Make sure that the volume level is set to produce sound from the headphones. If not, use the slider to adjust the volume.