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linuxdebug/Documentation/admin-guide/media/dvb_intro.rst

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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