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Like CD-R, DVD has been extended for recording, but with two different formats, known as DVD-R and DVD+R. At the time of writing, both formats were popular, and some combo drives supported both formats. Similarly, a rewritable DVD has been developed — or rather, two different formats, known as DVD-RW and DVD+RW. Finally, a format known as DVD-RAM offers a random-access read/write media similar to hard disk storage.

DVD-ROM drives can be formatted with a (large) ISO 9660 filesystem, optionally with Rock Ridge or Joliet extensions. They often, however, use the UDF (Universal Disc Format) file system, which is used by DVD movies and is better suited to large storage media.

For applications where multimedia is to be sent live via the Internet, often broadcast to multiple users, sending entire files is not suitable. Streaming media refers to systems where audio, or other media, is sent and played back in real time.

Multimedia Hardware

Now that we've discussed digital audio concepts, let's look at the hardware used. Sound cards follow a similar history as other peripheral cards for PCs. The first-generation cards used the ISA bus, and most aimed to be compatible with the Sound Blaster series from Creative Labs. The introduction of the ISA Plug and Play (PNP) standard allowed many sound cards to adopt this format and simplify configuration by eliminating the need for hardware jumpers. Modern sound cards now typically use the PCI bus, either as separate peripheral cards or as on-board sound hardware that resides on the motherboard but is accessed through the PCI bus. USB sound devices are also now available, some providing traditional sound card functions as well as peripherals such as loudspeakers that can be controlled through the USB bus.

Some sound cards now support higher-end features such as surround sound using as many as six sound channels, and digital inputs and outputs that can connect to home theater systems. This is beyond the scope of what can be covered in this chapter.

In the realm of video, there is obviously the ubiquitous video card, many of which offer 3D acceleration, large amounts of on-board memory, and sometimes more than one video output (multi-head).

TV tuner cards can decode television signals and output them to a video monitor, often via a video card so the image can be mixed with the computer video. Video capture cards can record video in real time for storage on hard disk and later playback.

Although the mouse and keyboard are the most common input devices, Linux also supports a number of touch screens, digitizing tablets, and joysticks.

Many scanners are supported on Linux. Older models generally use a SCSI or parallel port interface. Some of these use proprietary protocols and are not supported on Linux. Newer scanners tend to use USB, although some high-end professional models instead use FireWire (Apple's term for a standard also known as IEEE 1394) for higher throughput.

Digital cameras have had some support under Linux, improving over time as more drivers are developed and cameras move to more standardized protocols. Older models used serial and occasionally SCSI interfaces. Newer units employ USB if they provide a direct cable interface at all. They also generally use one of several standard flash memory modules, which can be removed and read on a computer with a suitable adapter that connects to a USB or PCMCIA port. With the adoption of a standard USB mass storage protocol, all compliant devices should be supported under Linux. The Linux kernel represents USB mass storage devices as if they were SCSI devices.

Kernel and Driver Issues

Configuring and building the kernel is covered elsewhere in this book. We cover here a few points relevant to multimedia . As mentioned earlier, most multimedia cards use the PCI bus and should be automatically detected and configured by the Linux kernel.

Sound Drivers

The history of sound drivers under Linux deserves some mention here, because it helps