Analogue TV is the predecessor of DVB. It is expected that the various global analogue TV systems will eventually all be replaced in favour of the newer digital TV systems. In some countries, such as Germany for example, analogue TV is no longer available, having been completely replaced by DVB-T (in the case of terrestrial broadcasts). In many other countries, the transition to digital is expected to occur much more slowly, and both analogue and digital TV systems will operate concurrently for some time to come. Yet still, in other countries, the switch to a digital TV system hasn't even begun, or is only in a trial phase, and, thus, an analogue TV system remains the relevant distribution method for transmissions in that locality.
Regardless of the actual schedule or pace for the transition to digital, the analogue TV standards will maintain considerable relevance into the foreseeable future due to their interrelatedness with the analogue outputs found on many types of existing consumer hardware; such as analogue camcorders, VCR/VHS players, most DVD players and so forth. Thus, even when analogue TV tuner devices will eventually only be able to pick up static off the airwaves (i.e. rendered completely obsolete), there will likely still be plenty of interest in using the analogue input signal facilities offered by framegrabber devices.
Analogue TV Standards
ITU-T defines monochrome television systems designated A, B, C, D, E, F, G, H, I, K, L, M, N. (A, C, E and F are no longer in use). They are esentially the same, but differ in the number of lines per field (405/525/625/819), frame rate (25/29.97), channel width, visual band width, vestigial band width, video modulation polarity (+/-), sound modulation type (AM/FM) and sound frequency offset (-6.5/-3.5/+4.5/+5.5/+5.996/+6.5/+13.5 MHz).
A summary of the monochromatic standards is provided in the following table:
|Number of lines||405||625||625||625||819||819||625||625||625||625||625||525||625|
|Field Rate (Hz)||50||50||50||50||50||50||50||50||50||50||50||59.94||50|
|Frame Rate (Hz)||25||25||25||25||25||25||25||25||25||25||25||29.97||25|
| Color Subcarrier Frequency
(on associated color std)
|-||4.43 MHz||-||4.43 MHz||-||-||4.43 MHz||4.43 MHz||4.43 MHz||4.406 MHz||4.406 MHz|| 3.579545 MHz (NTSC) |
3.575611 MHz (PAL)
|Channel Bandwidth (MHz)||5||7||7||8||14||7||8||8||8||8||8||6||6|
A color TV system is obtained by adding a color subcarrier encoded by one of the three color systems: PAL, SECAM or NTSC. Theoretically one can combine any picture system with any color system. In practice only some combinations are used. The frequency of the color subcarrier is generally
Example: PAL-I, the I television system with PAL color is used in Britain.
SECAM (Sequential Couleur A Mémoire) is a color standard used on France, Russia, and few countries at Central, East Europe, America, Africa and Asia. It is generally associated with monochromatic standards B, G, D, K and L (so, its typical resolution is 625 Lines, 25 frames per second). See SECAM page on Wikipedia for much more detail.
NTSC (National Television System Committee) is used in USA, Canada, and Japan. It is generally associated with monochromatic standard M (NTSC/M), so, its typical resolution is 525 Lines, about 30 frames per second. Less quality then PAL, therefore sometimes called Never Twice the Same Color, since the colors can shift as the phase of the color subcarrier shifts on broadcast. ;-) See NTSC page on Wikipedia for much more detail.
PAL (Phase Alternating Line) is the most widely used color standard for analog TV in the world, used almost everywhere. It is generally associated with monochromatic standards with a resolution of 625 Lines, 50 half frames per second. It can also be associated with M standard (PAL/M), having a resolution of 525 lines, about 30 frames per second. It is generally associated with 4:3 aspect. There is a 16:9 extension of PAL called PALplus. See PAL page on Wikipedia for much more detail.
Hardware Devices supporting Analog TV and/or Framegrabbing facilities
A large number of devices are supported under Linux with which an analogue source signal (analogue TV transmission or otherwise, such as from an A/V output from a consumer device like a DVD player) can be inputted into a host computer system. Some examples of which can be found under:
- Conexant (Brooktree) based analog TV cards using the bttv driver - very stable, good support but no hardware MPEG Encoder;
- Conexant cx18 driver - it is a recent driver. Supports analog and digital TV. It also supports MPEG encoder;
- Conexant cx88 driver - stable, good support. A few boards have MPEG encoder;
- Conexant ivtv driver = supports Hauppauge and similar cards based on the cx23415/cx23416 chip. These cards are really good and have an onboard MPEG encoder (both cards) and an MPEG decoder with TV-out (PVR 350 only).
- NXP (Philips semicondutor) saa7134 driver - stable, good support. A few boards have MPEG encoder. Supports saa7130, saa7131, saa7133, saa7134 and saa7135 devices;
- NXP (Philips semicondutor) saa7146 driver - stable.
- Zoran driver - stable.
- Zoran 36120 driver - driver broken kernels 2.6. Removed due to that.
- Empia em28xx driver - stable, good support.
- Hauppauge PVR USB2 pvrusb2 driver - stable, good support.
- Trident tm5600/tm6000/tm6010 tm5600 driver - currently being developed. Not working yet.
- Nogatech NT1003/1004/1005 usbvision driver - stable, good support.