Radio and TV Tuners

An alternative to cameras for video input comes in the form of audio/video input boards. These products usually include a TV tuner; the capacity to process raw video from a VCR, camcorder, or other device; and often an AM/FM radio tuner. These products vary along many of the same dimensions as do ordinary TVs and VCRs, such as

• Number of channels Some tuners can handle more channels than others can, which is an important consideration if you want to capture video from a cable TV station with a high number.

• Stereo Low-cost products process only mono sound, whereas more expensive products decode stereo sound.

• Video inputs Some products accept only a coaxial cable input, which enables connection to cable TV systems or a VCR's antenna output. Others include RCA jacks or S-video inputs, for processing higher-quality signals. A well-outfitted card sports quite a wide array of input and output jacks, as shown in Figure 13.4.

• Video signals Broadcast TV signals in North America follow the National Television Standards Committee (NTSC) convention, but signals in Europe and elsewhere follow the Phase Alternating Line (PAL) or Sequential Color and Memory (SECAM) standards. Some video decoder cards can handle all three standards, but others are more limited. Similarly, a few cards can receive AM or FM radio broadcasts, but others can't.

NOTE

Radio-only cards also exist. Oddly enough, these devices use the Video for Linux drivers and interfaces, although they aren't video devices at all. From a Linux driver and applications point of view, you can treat them as if they were TV cards, except that they produce no video image.

Chapter 13

Figure 13.4

A video input card contains input jacks similar to those on a TV or VCR.

Figure 13.4

A video input card contains input jacks similar to those on a TV or VCR.

Products also vary in ways that don't correspond to features on conventional TVs or VCRs, such as

• Interface method Most products use the PCI or ISA busses, but a few are external to the computer and interface via the USB port. Some internal products require the use of a video card's expansion connector, but others don't.

• Resolutions Conventional NTSC, PAL, and SECAM broadcasts don't use precise digital resolutions. The video decoder products must therefore convert to a conventional computer resolution. The range of supported target resolutions varies from one product to another. Beyond 640x480 or thereabouts, however, little or nothing is gained in picture quality; only image size increases at higher resolutions.

TV tuners and video input devices rely upon the Video for Linux device drivers included with the kernel, and upon specialized TV viewing and video extraction tools described later in this chapter. Because these devices require such specialized drivers, it's critical that you check for

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