TV card
A TV card , also known as television card or television adapter, is a general term for various expansion cards or plug-in adapters that are used to display television signals via the computer on the computer monitor or to record them on data storage media that can be written to in various ways, such as hard disk drives , USB mass storage devices or solid state drives . With the advent of the first television cards, beginning in the 1990s and up to around 2010, larger plug-in cards with interfaces such as the PCI or PCI Express interface or smaller designs in the form of an ExpressCard were common, but these became increasingly common in the following years thanks to compact television adapters with USB -Interface replaced.
In principle, television cards include the tuner required for reception and the subsequent decoding and processing of the television signals, including a suitable interface to the PC, often supplemented with an interface for an infrared remote control . The antennas required for terrestrial or satellite reception are not included; alternatively, a cable television connection can be used, and in contrast to television sets , the device components required for outputting or storing image and sound signals, which are part of the computer system, are also missing.
A distinction must be made between frame grabbers and TV cards, which evaluate video signals in the baseband like the FBAS signal in the analog range and represent the interface for video processing on the PC. The main differentiator is that frame grabbers do not have a built-in tuner.
Types
Depending on the range of functions and technological developments, television cards have different characteristics and support different television standards. TV cards can be roughly divided into support of analog and / or digital video standards. In addition to analog and / or digital TV reception, some TV cards have additional reception options , for example classic Cinch or S-Video inputs or an HDMI input.
Analog television cards
Analog television cards dominated in the early days until the mid-2000s, when television programs were primarily broadcast in the analog television standards. These were analog video transmission methods such as PAL , which was primarily used in Europe, and NTSC , primarily in North America. Terrestrial television reception and reception via cable network operators were technically identical. Many of these analog television cards also offered the option of receiving analog VHF radio in the frequency range from 88.5 MHz to 108 MHz and outputting it through the loudspeakers of a PC.
Some of the first analog TV cards of the first generation, which are also known as video overlay cards, generate the analog VGA signal for the monitor itself and mix it with the analog VGA signal from the graphics card. This was due to the fact that the PC systems with ISA bus at the time were not powerful enough for the time-critical transport of digital video data between TV card and video card. The disadvantage of the method is that the quality of the display of the graphic is reduced by the signal mixing.
Some analog TV cards also offer the function of genlock . This enables an analog video signal to be output and text or images to be displayed in synchronism with the TV image received. The chipsets used in analog TV cards , which are supported by many operating systems, are from Conexant (formerly Brooktree ) with the designations Bt848 / 849/878/879.
Digital television cards
With the replacement of analog television program transmission by digital processes such as DVB-T and DVB-T2 for terrestrial reception, DVB-C for digital cable reception and DVB-S and DVB-S2 for satellite reception, the television cards were also adapted. Depending on the type, combinations of the various digital television standards are available in one card, and because of the similarity of names, they are also known as DVB cards . For DVB-T2 receivers in particular, the combination with DVB-C (as well as downward compatibility with DVB-T) is common because they use the same frequencies and bandwidths. The first digital TV cards had a hardware-supported MPEG-2 decoder, later models also include decoders for H.264 and H.265 . However, such cards can be found in the upper price ranges. This has been becoming increasingly obsolete since around 2016, as current CPUs already contain this function.
In order to record a program, the data stream from a digital TV card only needs to be saved on a data carrier, usually a hard drive because of the required storage capacity and writing speed. In contrast to this, when recording using an analog TV card, the analog video and audio signals must be digitized and compressed in real time by the PC, which is a complex process, and then saved on a data carrier. Recording via a digital TV card is therefore always of the highest quality regardless of the make. Only disturbances on the transmission path from satellite, terrestrial transmitters or disturbances in the TV cable network reduce the quality, which manifests itself in picture and sound dropouts or "pixelated" pictures ("blocks" in the picture). The demands on the computer are also significantly lower, which avoids dropouts on computers with lower computing power. However, the recording function may be restricted by digital rights management .
The dimensions of classic television cards are getting smaller and smaller due to the advancing miniaturization of electronics. While terrestrial receivers have been connected via USB for a long time (see DVB-T stick ), as of 2015 other digital TV cards are increasingly equipped with a USB interface and allow easy connection to various computers such as laptops or single-board computers such as the Raspberry Pi . While cable and antenna receivers get by with power from a USB connection, USB satellite receivers, unlike internal variants, require an additional power supply, usually through an external power supply unit.
literature
- Björn Walter: Audio / Video Recording on the PC: Record and save everything digitally . Pearson, 2004, ISBN 978-3-8272-6734-4 , chapter 1.
