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SPDX-License-Identifier: GPL-2.0 ============================== Using the Digital TV Framework ============================== Introduction ~~~~~~~~~~~~ One significant difference between Digital TV and Analogue TV that the unwary (like myself) should consider is that, although the component structure of DVB-T cards are substantially similar to Analogue TV cards, they function in substantially different ways. The purpose of an Analogue TV is to receive and display an Analogue Television signal. An Analogue TV signal (otherwise known as composite video) is an analogue encoding of a sequence of image frames (25 frames per second in Europe) rasterised using an interlacing technique. Interlacing takes two fields to represent one frame. Therefore, an Analogue TV card for a PC has the following purpose: * Tune the receiver to receive a broadcast signal * demodulate the broadcast signal * demultiplex the analogue video signal and analogue audio signal. .. note:: some countries employ a digital audio signal embedded within the modulated composite analogue signal - using NICAM signaling.) * digitize the analogue video signal and make the resulting datastream available to the data bus. The digital datastream from an Analogue TV card is generated by circuitry on the card and is often presented uncompressed. For a PAL TV signal encoded at a resolution of 768x576 24-bit color pixels over 25 frames per second - a fair amount of data is generated and must be processed by the PC before it can be displayed on the video monitor screen. Some Analogue TV cards for PCs have onboard MPEG2 encoders which permit the raw digital data stream to be presented to the PC in an encoded and compressed form - similar to the form that is used in Digital TV. The purpose of a simple budget digital TV card (DVB-T,C or S) is to simply: * Tune the received to receive a broadcast signal. * Extract the encoded digital datastream from the broadcast signal. * Make the encoded digital datastream (MPEG2) available to the data bus. The significant difference between the two is that the tuner on the analogue TV card spits out an Analogue signal, whereas the tuner on the digital TV card spits out a compressed encoded digital datastream. As the signal is already digitised, it is trivial to pass this datastream to the PC databus with minimal additional processing and then extract the digital video and audio datastreams passing them to the appropriate software or hardware for decoding and viewing. Getting the card going ~~~~~~~~~~~~~~~~~~~~~~ The Device Driver API for DVB under Linux will the following device nodes via the devfs filesystem: * /dev/dvb/adapter0/demux0 * /dev/dvb/adapter0/dvr0 * /dev/dvb/adapter0/frontend0 The ``/dev/dvb/adapter0/dvr0`` device node is used to read the MPEG2 Data Stream and the ``/dev/dvb/adapter0/frontend0`` device node is used to tune the frontend tuner module. The ``/dev/dvb/adapter0/demux0`` is used to control what programs will be received. Depending on the card's feature set, the Device Driver API could also expose other device nodes: * /dev/dvb/adapter0/ca0 * /dev/dvb/adapter0/audio0 * /dev/dvb/adapter0/net0 * /dev/dvb/adapter0/osd0 * /dev/dvb/adapter0/video0 The ``/dev/dvb/adapter0/ca0`` is used to decode encrypted channels. The other device nodes are found only on devices that use the av7110 driver, with is now obsoleted, together with the extra API whose such devices use. Receiving a digital TV channel ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ This section attempts to explain how it works and how this affects the configuration of a Digital TV card. On this example, we're considering tuning into DVB-T channels in Australia, at the Melbourne region. The frequencies broadcast by Mount Dandenong transmitters are, currently: Table 1. Transponder Frequencies Mount Dandenong, Vic, Aus. =========== =========== Broadcaster Frequency =========== =========== Seven 177.500 Mhz SBS 184.500 Mhz Nine 191.625 Mhz Ten 219.500 Mhz ABC 226.500 Mhz Channel 31 557.625 Mhz =========== =========== The digital TV Scan utilities (like dvbv5-scan) have use a set of compiled-in defaults for various countries and regions. Those are currently provided as a separate package, called dtv-scan-tables. It's git tree is located at LinuxTV.org: https://git.linuxtv.org/dtv-scan-tables.git/ If none of the tables there suit, you can specify a data file on the command line which contains the transponder frequencies. Here is a sample file for the above channel transponders, in the old "channel" format:: # Data file for DVB scan program # # C Frequency SymbolRate FEC QAM # S Frequency Polarisation SymbolRate FEC # T Frequency Bandwidth FEC FEC2 QAM Mode Guard Hier T 177500000 7MHz AUTO AUTO QAM64 8k 1/16 NONE T 184500000 7MHz AUTO AUTO QAM64 8k 1/8 NONE T 191625000 7MHz AUTO AUTO QAM64 8k 1/16 NONE T 219500000 7MHz AUTO AUTO QAM64 8k 1/16 NONE T 226500000 7MHz AUTO AUTO QAM64 8k 1/16 NONE T 557625000 7MHz AUTO AUTO QPSK 8k 1/16 NONE Nowadays, we prefer to use a newer format, with is more verbose and easier to understand. With the new format, the "Seven" channel transponder's data is represented by:: [Seven] DELIVERY_SYSTEM = DVBT FREQUENCY = 177500000 BANDWIDTH_HZ = 7000000 CODE_RATE_HP = AUTO CODE_RATE_LP = AUTO MODULATION = QAM/64 TRANSMISSION_MODE = 8K GUARD_INTERVAL = 1/16 HIERARCHY = NONE INVERSION = AUTO For an updated version of the complete table, please see: https://git.linuxtv.org/dtv-scan-tables.git/tree/dvb-t/au-Melbourne When the Digital TV scanning utility runs, it will output a file containing the information for all the audio and video programs that exists into each channel's transponders which the card's frontend can lock onto. (i.e. any whose signal is strong enough at your antenna). Here's the output of the dvbv5 tools from a channel scan took from Melburne:: [ABC HDTV] SERVICE_ID = 560 VIDEO_PID = 2307 AUDIO_PID = 0 DELIVERY_SYSTEM = DVBT FREQUENCY = 226500000 INVERSION = OFF BANDWIDTH_HZ = 7000000 CODE_RATE_HP = 3/4 CODE_RATE_LP = 3/4 MODULATION = QAM/64 TRANSMISSION_MODE = 8K GUARD_INTERVAL = 1/16 HIERARCHY = NONE [ABC TV Melbourne] SERVICE_ID = 561 VIDEO_PID = 512 AUDIO_PID = 650 DELIVERY_SYSTEM = DVBT FREQUENCY = 226500000 INVERSION = OFF BANDWIDTH_HZ = 7000000 CODE_RATE_HP = 3/4 CODE_RATE_LP = 3/4 MODULATION = QAM/64 TRANSMISSION_MODE = 8K GUARD_INTERVAL = 1/16 HIERARCHY = NONE [ABC TV 2] SERVICE_ID = 562 VIDEO_PID = 512 AUDIO_PID = 650 DELIVERY_SYSTEM = DVBT FREQUENCY = 226500000 INVERSION = OFF BANDWIDTH_HZ = 7000000 CODE_RATE_HP = 3/4 CODE_RATE_LP = 3/4 MODULATION = QAM/64 TRANSMISSION_MODE = 8K GUARD_INTERVAL = 1/16 HIERARCHY = NONE [ABC TV 3] SERVICE_ID = 563 VIDEO_PID = 512 AUDIO_PID = 650 DELIVERY_SYSTEM = DVBT FREQUENCY = 226500000 INVERSION = OFF BANDWIDTH_HZ = 7000000 CODE_RATE_HP = 3/4 CODE_RATE_LP = 3/4 MODULATION = QAM/64 TRANSMISSION_MODE = 8K GUARD_INTERVAL = 1/16 HIERARCHY = NONE [ABC TV 4] SERVICE_ID = 564 VIDEO_PID = 512 AUDIO_PID = 650 DELIVERY_SYSTEM = DVBT FREQUENCY = 226500000 INVERSION = OFF BANDWIDTH_HZ = 7000000 CODE_RATE_HP = 3/4 CODE_RATE_LP = 3/4 MODULATION = QAM/64 TRANSMISSION_MODE = 8K GUARD_INTERVAL = 1/16 HIERARCHY = NONE [ABC DiG Radio] SERVICE_ID = 566 VIDEO_PID = 0 AUDIO_PID = 2311 DELIVERY_SYSTEM = DVBT FREQUENCY = 226500000 INVERSION = OFF BANDWIDTH_HZ = 7000000 CODE_RATE_HP = 3/4 CODE_RATE_LP = 3/4 MODULATION = QAM/64 TRANSMISSION_MODE = 8K GUARD_INTERVAL = 1/16 HIERARCHY = NONE [TEN Digital] SERVICE_ID = 1585 VIDEO_PID = 512 AUDIO_PID = 650 DELIVERY_SYSTEM = DVBT FREQUENCY = 219500000 INVERSION = OFF BANDWIDTH_HZ = 7000000 CODE_RATE_HP = 3/4 CODE_RATE_LP = 1/2 MODULATION = QAM/64 TRANSMISSION_MODE = 8K GUARD_INTERVAL = 1/16 HIERARCHY = NONE [TEN Digital 1] SERVICE_ID = 1586 VIDEO_PID = 512 AUDIO_PID = 650 DELIVERY_SYSTEM = DVBT FREQUENCY = 219500000 INVERSION = OFF BANDWIDTH_HZ = 7000000 CODE_RATE_HP = 3/4 CODE_RATE_LP = 1/2 MODULATION = QAM/64 TRANSMISSION_MODE = 8K GUARD_INTERVAL = 1/16 HIERARCHY = NONE [TEN Digital 2] SERVICE_ID = 1587 VIDEO_PID = 512 AUDIO_PID = 650 DELIVERY_SYSTEM = DVBT FREQUENCY = 219500000 INVERSION = OFF BANDWIDTH_HZ = 7000000 CODE_RATE_HP = 3/4 CODE_RATE_LP = 1/2 MODULATION = QAM/64 TRANSMISSION_MODE = 8K GUARD_INTERVAL = 1/16 HIERARCHY = NONE [TEN Digital 3] SERVICE_ID = 1588 VIDEO_PID = 512 AUDIO_PID = 650 DELIVERY_SYSTEM = DVBT FREQUENCY = 219500000 INVERSION = OFF BANDWIDTH_HZ = 7000000 CODE_RATE_HP = 3/4 CODE_RATE_LP = 1/2 MODULATION = QAM/64 TRANSMISSION_MODE = 8K GUARD_INTERVAL = 1/16 HIERARCHY = NONE [TEN Digital] SERVICE_ID = 1589 VIDEO_PID = 512 AUDIO_PID = 650 DELIVERY_SYSTEM = DVBT FREQUENCY = 219500000 INVERSION = OFF BANDWIDTH_HZ = 7000000 CODE_RATE_HP = 3/4 CODE_RATE_LP = 1/2 MODULATION = QAM/64 TRANSMISSION_MODE = 8K GUARD_INTERVAL = 1/16 HIERARCHY = NONE [TEN Digital 4] SERVICE_ID = 1590 VIDEO_PID = 512 AUDIO_PID = 650 DELIVERY_SYSTEM = DVBT FREQUENCY = 219500000 INVERSION = OFF BANDWIDTH_HZ = 7000000 CODE_RATE_HP = 3/4 CODE_RATE_LP = 1/2 MODULATION = QAM/64 TRANSMISSION_MODE = 8K GUARD_INTERVAL = 1/16 HIERARCHY = NONE [TEN Digital] SERVICE_ID = 1591 VIDEO_PID = 512 AUDIO_PID = 650 DELIVERY_SYSTEM = DVBT FREQUENCY = 219500000 INVERSION = OFF BANDWIDTH_HZ = 7000000 CODE_RATE_HP = 3/4 CODE_RATE_LP = 1/2 MODULATION = QAM/64 TRANSMISSION_MODE = 8K GUARD_INTERVAL = 1/16 HIERARCHY = NONE [TEN HD] SERVICE_ID = 1592 VIDEO_PID = 514 AUDIO_PID = 0 DELIVERY_SYSTEM = DVBT FREQUENCY = 219500000 INVERSION = OFF BANDWIDTH_HZ = 7000000 CODE_RATE_HP = 3/4 CODE_RATE_LP = 1/2 MODULATION = QAM/64 TRANSMISSION_MODE = 8K GUARD_INTERVAL = 1/16 HIERARCHY = NONE [TEN Digital] SERVICE_ID = 1593 VIDEO_PID = 512 AUDIO_PID = 650 DELIVERY_SYSTEM = DVBT FREQUENCY = 219500000 INVERSION = OFF BANDWIDTH_HZ = 7000000 CODE_RATE_HP = 3/4 CODE_RATE_LP = 1/2 MODULATION = QAM/64 TRANSMISSION_MODE = 8K GUARD_INTERVAL = 1/16 HIERARCHY = NONE [Nine Digital] SERVICE_ID = 1072 VIDEO_PID = 513 AUDIO_PID = 660 DELIVERY_SYSTEM = DVBT FREQUENCY = 191625000 INVERSION = OFF BANDWIDTH_HZ = 7000000 CODE_RATE_HP = 3/4 CODE_RATE_LP = 1/2 MODULATION = QAM/64 TRANSMISSION_MODE = 8K GUARD_INTERVAL = 1/16 HIERARCHY = NONE [Nine Digital HD] SERVICE_ID = 1073 VIDEO_PID = 512 AUDIO_PID = 0 DELIVERY_SYSTEM = DVBT FREQUENCY = 191625000 INVERSION = OFF BANDWIDTH_HZ = 7000000 CODE_RATE_HP = 3/4 CODE_RATE_LP = 1/2 MODULATION = QAM/64 TRANSMISSION_MODE = 8K GUARD_INTERVAL = 1/16 HIERARCHY = NONE [Nine Guide] SERVICE_ID = 1074 VIDEO_PID = 514 AUDIO_PID = 670 DELIVERY_SYSTEM = DVBT FREQUENCY = 191625000 INVERSION = OFF BANDWIDTH_HZ = 7000000 CODE_RATE_HP = 3/4 CODE_RATE_LP = 1/2 MODULATION = QAM/64 TRANSMISSION_MODE = 8K GUARD_INTERVAL = 1/16 HIERARCHY = NONE [7 Digital] SERVICE_ID = 1328 VIDEO_PID = 769 AUDIO_PID = 770 DELIVERY_SYSTEM = DVBT FREQUENCY = 177500000 INVERSION = OFF BANDWIDTH_HZ = 7000000 CODE_RATE_HP = 2/3 CODE_RATE_LP = 2/3 MODULATION = QAM/64 TRANSMISSION_MODE = 8K GUARD_INTERVAL = 1/8 HIERARCHY = NONE [7 Digital 1] SERVICE_ID = 1329 VIDEO_PID = 769 AUDIO_PID = 770 DELIVERY_SYSTEM = DVBT FREQUENCY = 177500000 INVERSION = OFF BANDWIDTH_HZ = 7000000 CODE_RATE_HP = 2/3 CODE_RATE_LP = 2/3 MODULATION = QAM/64 TRANSMISSION_MODE = 8K GUARD_INTERVAL = 1/8 HIERARCHY = NONE [7 Digital 2] SERVICE_ID = 1330 VIDEO_PID = 769 AUDIO_PID = 770 DELIVERY_SYSTEM = DVBT FREQUENCY = 177500000 INVERSION = OFF BANDWIDTH_HZ = 7000000 CODE_RATE_HP = 2/3 CODE_RATE_LP = 2/3 MODULATION = QAM/64 TRANSMISSION_MODE = 8K GUARD_INTERVAL = 1/8 HIERARCHY = NONE [7 Digital 3] SERVICE_ID = 1331 VIDEO_PID = 769 AUDIO_PID = 770 DELIVERY_SYSTEM = DVBT FREQUENCY = 177500000 INVERSION = OFF BANDWIDTH_HZ = 7000000 CODE_RATE_HP = 2/3 CODE_RATE_LP = 2/3 MODULATION = QAM/64 TRANSMISSION_MODE = 8K GUARD_INTERVAL = 1/8 HIERARCHY = NONE [7 HD Digital] SERVICE_ID = 1332 VIDEO_PID = 833 AUDIO_PID = 834 DELIVERY_SYSTEM = DVBT FREQUENCY = 177500000 INVERSION = OFF BANDWIDTH_HZ = 7000000 CODE_RATE_HP = 2/3 CODE_RATE_LP = 2/3 MODULATION = QAM/64 TRANSMISSION_MODE = 8K GUARD_INTERVAL = 1/8 HIERARCHY = NONE [7 Program Guide] SERVICE_ID = 1334 VIDEO_PID = 865 AUDIO_PID = 866 DELIVERY_SYSTEM = DVBT FREQUENCY = 177500000 INVERSION = OFF BANDWIDTH_HZ = 7000000 CODE_RATE_HP = 2/3 CODE_RATE_LP = 2/3 MODULATION = QAM/64 TRANSMISSION_MODE = 8K GUARD_INTERVAL = 1/8 HIERARCHY = NONE [SBS HD] SERVICE_ID = 784 VIDEO_PID = 102 AUDIO_PID = 103 DELIVERY_SYSTEM = DVBT FREQUENCY = 536500000 INVERSION = OFF BANDWIDTH_HZ = 7000000 CODE_RATE_HP = 2/3 CODE_RATE_LP = 2/3 MODULATION = QAM/64 TRANSMISSION_MODE = 8K GUARD_INTERVAL = 1/8 HIERARCHY = NONE [SBS DIGITAL 1] SERVICE_ID = 785 VIDEO_PID = 161 AUDIO_PID = 81 DELIVERY_SYSTEM = DVBT FREQUENCY = 536500000 INVERSION = OFF BANDWIDTH_HZ = 7000000 CODE_RATE_HP = 2/3 CODE_RATE_LP = 2/3 MODULATION = QAM/64 TRANSMISSION_MODE = 8K GUARD_INTERVAL = 1/8 HIERARCHY = NONE [SBS DIGITAL 2] SERVICE_ID = 786 VIDEO_PID = 162 AUDIO_PID = 83 DELIVERY_SYSTEM = DVBT FREQUENCY = 536500000 INVERSION = OFF BANDWIDTH_HZ = 7000000 CODE_RATE_HP = 2/3 CODE_RATE_LP = 2/3 MODULATION = QAM/64 TRANSMISSION_MODE = 8K GUARD_INTERVAL = 1/8 HIERARCHY = NONE [SBS EPG] SERVICE_ID = 787 VIDEO_PID = 163 AUDIO_PID = 85 DELIVERY_SYSTEM = DVBT FREQUENCY = 536500000 INVERSION = OFF BANDWIDTH_HZ = 7000000 CODE_RATE_HP = 2/3 CODE_RATE_LP = 2/3 MODULATION = QAM/64 TRANSMISSION_MODE = 8K GUARD_INTERVAL = 1/8 HIERARCHY = NONE [SBS RADIO 1] SERVICE_ID = 798 VIDEO_PID = 0 AUDIO_PID = 201 DELIVERY_SYSTEM = DVBT FREQUENCY = 536500000 INVERSION = OFF BANDWIDTH_HZ = 7000000 CODE_RATE_HP = 2/3 CODE_RATE_LP = 2/3 MODULATION = QAM/64 TRANSMISSION_MODE = 8K GUARD_INTERVAL = 1/8 HIERARCHY = NONE [SBS RADIO 2] SERVICE_ID = 799 VIDEO_PID = 0 AUDIO_PID = 202 DELIVERY_SYSTEM = DVBT FREQUENCY = 536500000 INVERSION = OFF BANDWIDTH_HZ = 7000000 CODE_RATE_HP = 2/3 CODE_RATE_LP = 2/3 MODULATION = QAM/64 TRANSMISSION_MODE = 8K GUARD_INTERVAL = 1/8 HIERARCHY = NONE |