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203 lines
10 KiB
ReStructuredText
203 lines
10 KiB
ReStructuredText
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.. SPDX-License-Identifier: GPL-2.0
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==============================
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Using the Digital TV Framework
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==============================
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February 14th 2006
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Introduction
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~~~~~~~~~~~~
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.. note::
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This documentation is outdated. Please check at the DVB wiki
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at https://linuxtv.org/wiki for more updated info.
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There's a section there specific for Avermedia boards at:
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https://linuxtv.org/wiki/index.php/AVerMedia
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Assumptions and Introduction
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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It is assumed that the reader understands the basic structure
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of the Linux Kernel DVB drivers and the general principles of
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Digital TV.
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One significant difference between Digital TV and Analogue TV
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that the unwary (like myself) should consider is that,
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although the component structure of budget DVB-T cards are
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substantially similar to Analogue TV cards, they function in
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substantially different ways.
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The purpose of an Analogue TV is to receive and display an
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Analogue Television signal. An Analogue TV signal (otherwise
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known as composite video) is an analogue encoding of a
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sequence of image frames (25 per second) rasterised using an
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interlacing technique. Interlacing takes two fields to
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represent one frame. Computers today are at their best when
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dealing with digital signals, not analogue signals and a
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composite video signal is about as far removed from a digital
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data stream as you can get. Therefore, an Analogue TV card for
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a PC has the following purpose:
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* Tune the receiver to receive a broadcast signal
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* demodulate the broadcast signal
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* demultiplex the analogue video signal and analogue audio
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signal. **NOTE:** some countries employ a digital audio signal
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embedded within the modulated composite analogue signal -
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NICAM.)
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* digitize the analogue video signal and make the resulting
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datastream available to the data bus.
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The digital datastream from an Analogue TV card is generated
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by circuitry on the card and is often presented uncompressed.
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For a PAL TV signal encoded at a resolution of 768x576 24-bit
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color pixels over 25 frames per second - a fair amount of data
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is generated and must be processed by the PC before it can be
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displayed on the video monitor screen. Some Analogue TV cards
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for PCs have onboard MPEG2 encoders which permit the raw
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digital data stream to be presented to the PC in an encoded
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and compressed form - similar to the form that is used in
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Digital TV.
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The purpose of a simple budget digital TV card (DVB-T,C or S)
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is to simply:
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* Tune the received to receive a broadcast signal.
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* Extract the encoded digital datastream from the broadcast
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signal.
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* Make the encoded digital datastream (MPEG2) available to
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the data bus.
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The significant difference between the two is that the tuner
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on the analogue TV card spits out an Analogue signal, whereas
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the tuner on the digital TV card spits out a compressed
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encoded digital datastream. As the signal is already
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digitised, it is trivial to pass this datastream to the PC
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databus with minimal additional processing and then extract
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the digital video and audio datastreams passing them to the
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appropriate software or hardware for decoding and viewing.
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Getting the card going
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~~~~~~~~~~~~~~~~~~~~~~
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In order to fire up the card, it is necessary to load a number
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of modules from the DVB driver set. Prior to this it will have
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been necessary to download these drivers from the linuxtv CVS
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server and compile them successfully.
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Depending on the card's feature set, the Device Driver API for
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DVB under Linux will expose some of the following device files
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in the /dev tree:
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* /dev/dvb/adapter0/audio0
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* /dev/dvb/adapter0/ca0
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* /dev/dvb/adapter0/demux0
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* /dev/dvb/adapter0/dvr0
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* /dev/dvb/adapter0/frontend0
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* /dev/dvb/adapter0/net0
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* /dev/dvb/adapter0/osd0
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* /dev/dvb/adapter0/video0
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The primary device nodes that we are interested in (at this
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stage) for the Avermedia DVB-T are:
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* /dev/dvb/adapter0/dvr0
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* /dev/dvb/adapter0/frontend0
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The dvr0 device node is used to read the MPEG2 Data Stream and
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the frontend0 node is used to tune the frontend tuner module.
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Receiving DVB-T in Australia
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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I have no experience of DVB-T in other countries other than
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Australia, so I will attempt to explain how it works here in
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Melbourne and how this affects the configuration of the DVB-T
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card.
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The Digital Broadcasting Australia website has a Reception
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locatortool which provides information on transponder channels
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and frequencies. My local transmitter happens to be Mount
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Dandenong.
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The frequencies broadcast by Mount Dandenong are:
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Table 1. Transponder Frequencies Mount Dandenong, Vic, Aus.
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=========== ======= ===========
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Broadcaster Channel Frequency
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=========== ======= ===========
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ABC VHF 12 226.5 MHz
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TEN VHF 11 219.5 MHz
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NINE VHF 8 191.625 MHz
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SEVEN VHF 6 177.5 MHz
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SBS UHF 29 536.5 MHz
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=========== ======= ===========
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The Scan utility has a set of compiled-in defaults for various
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countries and regions, but if they do not suit, or if you have
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a pre-compiled scan binary, you can specify a data file on the
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command line which contains the transponder frequencies. Here
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is a sample file for the above channel transponders:
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::
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# Data file for DVB scan program
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#
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# C Frequency SymbolRate FEC QAM
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# S Frequency Polarisation SymbolRate FEC
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# T Frequency Bandwidth FEC FEC2 QAM Mode Guard Hier
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T 226500000 7MHz 2/3 NONE QAM64 8k 1/8 NONE
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T 191625000 7MHz 2/3 NONE QAM64 8k 1/8 NONE
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T 219500000 7MHz 2/3 NONE QAM64 8k 1/8 NONE
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T 177500000 7MHz 2/3 NONE QAM64 8k 1/8 NONE
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T 536500000 7MHz 2/3 NONE QAM64 8k 1/8 NONE
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The defaults for the transponder frequency and other
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modulation parameters were obtained from www.dba.org.au.
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When Scan runs, it will output channels.conf information for
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any channel's transponders which the card's frontend can lock
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onto. (i.e. any whose signal is strong enough at your
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antenna).
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Here's my channels.conf file for anyone who's interested:
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::
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ABC HDTV:226500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_3_4:FEC_3_4:QAM_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_16:HIERARCHY_NONE:2307:0:560
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ABC TV Melbourne:226500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_3_4:FEC_3_4:QAM_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_16:HIERARCHY_NONE:512:650:561
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ABC TV 2:226500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_3_4:FEC_3_4:QAM_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_16:HIERARCHY_NONE:512:650:562
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ABC TV 3:226500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_3_4:FEC_3_4:QAM_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_16:HIERARCHY_NONE:512:650:563
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ABC TV 4:226500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_3_4:FEC_3_4:QAM_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_16:HIERARCHY_NONE:512:650:564
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ABC DiG Radio:226500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_3_4:FEC_3_4:QAM_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_16:HIERARCHY_NONE:0:2311:566
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TEN Digital:219500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_3_4:FEC_1_2:QAM_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_16:HIERARCHY_NONE:512:650:1585
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TEN Digital 1:219500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_3_4:FEC_1_2:QAM_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_16:HIERARCHY_NONE:512:650:1586
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TEN Digital 2:219500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_3_4:FEC_1_2:QAM_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_16:HIERARCHY_NONE:512:650:1587
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TEN Digital 3:219500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_3_4:FEC_1_2:QAM_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_16:HIERARCHY_NONE:512:650:1588
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TEN Digital:219500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_3_4:FEC_1_2:QAM_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_16:HIERARCHY_NONE:512:650:1589
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TEN Digital 4:219500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_3_4:FEC_1_2:QAM_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_16:HIERARCHY_NONE:512:650:1590
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TEN Digital:219500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_3_4:FEC_1_2:QAM_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_16:HIERARCHY_NONE:512:650:1591
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TEN HD:219500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_3_4:FEC_1_2:QAM_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_16:HIERARCHY_NONE:514:0:1592
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TEN Digital:219500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_3_4:FEC_1_2:QAM_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_16:HIERARCHY_NONE:512:650:1593
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Nine Digital:191625000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_3_4:FEC_1_2:QAM_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_16:HIERARCHY_NONE:513:660:1072
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Nine Digital HD:191625000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_3_4:FEC_1_2:QAM_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_16:HIERARCHY_NONE:512:0:1073
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Nine Guide:191625000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_3_4:FEC_1_2:QAM_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_16:HIERARCHY_NONE:514:670:1074
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7 Digital:177500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_2_3:FEC_2_3:QAM_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_8:HIERARCHY_NONE:769:770:1328
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7 Digital 1:177500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_2_3:FEC_2_3:QAM_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_8:HIERARCHY_NONE:769:770:1329
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7 Digital 2:177500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_2_3:FEC_2_3:QAM_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_8:HIERARCHY_NONE:769:770:1330
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7 Digital 3:177500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_2_3:FEC_2_3:QAM_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_8:HIERARCHY_NONE:769:770:1331
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7 HD Digital:177500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_2_3:FEC_2_3:QAM_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_8:HIERARCHY_NONE:833:834:1332
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7 Program Guide:177500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_2_3:FEC_2_3:QAM_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_8:HIERARCHY_NONE:865:866:1334
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SBS HD:536500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_2_3:FEC_2_3:QAM_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_8:HIERARCHY_NONE:102:103:784
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SBS DIGITAL 1:536500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_2_3:FEC_2_3:QAM_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_8:HIERARCHY_NONE:161:81:785
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SBS DIGITAL 2:536500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_2_3:FEC_2_3:QAM_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_8:HIERARCHY_NONE:162:83:786
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SBS EPG:536500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_2_3:FEC_2_3:QAM_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_8:HIERARCHY_NONE:163:85:787
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SBS RADIO 1:536500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_2_3:FEC_2_3:QAM_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_8:HIERARCHY_NONE:0:201:798
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SBS RADIO 2:536500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_2_3:FEC_2_3:QAM_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_8:HIERARCHY_NONE:0:202:799
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