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.. SPDX-License-Identifier: GPL-2.0
FAQ
===
.. note::
1. With Digital TV, a single physical channel may have different
contents inside it. The specs call each one as a *service*.
This is what a TV user would call "channel". So, in order to
avoid confusion, we're calling *transponders* as the physical
channel on this FAQ, and *services* for the logical channel.
2. The LinuxTV community maintains some Wiki pages with contain
a lot of information related to the media subsystem. If you
don't find an answer for your needs here, it is likely that
you'll be able to get something useful there. It is hosted
at:
https://www.linuxtv.org/wiki/
Some very frequently asked questions about Linux Digital TV support
1. The signal seems to die a few seconds after tuning.
It's not a bug, it's a feature. Because the frontends have
significant power requirements (and hence get very hot), they
are powered down if they are unused (i.e. if the frontend device
is closed). The ``dvb-core`` module parameter ``dvb_shutdown_timeout``
allow you to change the timeout (default 5 seconds). Setting the
timeout to 0 disables the timeout feature.
2. How can I watch TV?
Together with the Linux Kernel, the Digital TV developers support
some simple utilities which are mainly intended for testing
and to demonstrate how the DVB API works. This is called DVB v5
tools and are grouped together with the ``v4l-utils`` git repository:
https://git.linuxtv.org/v4l-utils.git/
You can find more information at the LinuxTV wiki:
https://www.linuxtv.org/wiki/index.php/DVBv5_Tools
The first step is to get a list of services that are transmitted.
This is done by using several existing tools. You can use
for example the ``dvbv5-scan`` tool. You can find more information
about it at:
https://www.linuxtv.org/wiki/index.php/Dvbv5-scan
There are some other applications like ``w_scan`` [#]_ that do a
blind scan, trying hard to find all possible channels, but
those consumes a large amount of time to run.
.. [#] https://www.linuxtv.org/wiki/index.php/W_scan
Also, some applications like ``kaffeine`` have their own code
to scan for services. So, you don't need to use an external
application to obtain such list.
Most of such tools need a file containing a list of channel
transponders available on your area. So, LinuxTV developers
maintain tables of Digital TV channel transponders, receiving
patches from the community to keep them updated.
This list is hosted at:
https://git.linuxtv.org/dtv-scan-tables.git
And packaged on several distributions.
Kaffeine has some blind scan support for some terrestrial standards.
It also relies on DTV scan tables, although it contains a copy
of it internally (and, if requested by the user, it will download
newer versions of it).
If you are lucky you can just use one of the supplied channel
transponders. If not, you may need to seek for such info at
the Internet and create a new file. There are several sites with
contains physical channel lists. For cable and satellite, usually
knowing how to tune into a single channel is enough for the
scanning tool to identify the other channels. On some places,
this could also work for terrestrial transmissions.
Once you have a transponders list, you need to generate a services
list with a tool like ``dvbv5-scan``.
Almost all modern Digital TV cards don't have built-in hardware
MPEG-decoders. So, it is up to the application to get a MPEG-TS
stream provided by the board, split it into audio, video and other
data and decode.
3. Which Digital TV applications exist?
Several media player applications are capable of tuning into
digital TV channels, including Kaffeine, Vlc, mplayer and MythTV.
Kaffeine aims to be very user-friendly, and it is maintained
by one of the Kernel driver developers.
A comprehensive list of those and other apps can be found at:
https://www.linuxtv.org/wiki/index.php/TV_Related_Software
Some of the most popular ones are linked below:
https://kde.org/applications/multimedia/org.kde.kaffeine
KDE media player, focused on Digital TV support
https://www.linuxtv.org/vdrwiki/index.php/Main_Page
Klaus Schmidinger's Video Disk Recorder
https://linuxtv.org/downloads and https://git.linuxtv.org/
Digital TV and other media-related applications and
Kernel drivers. The ``v4l-utils`` package there contains
several swiss knife tools for using with Digital TV.
http://sourceforge.net/projects/dvbtools/
Dave Chapman's dvbtools package, including
dvbstream and dvbtune
http://www.dbox2.info/
LinuxDVB on the dBox2
http://www.tuxbox.org/
the TuxBox CVS many interesting DVB applications and the dBox2
DVB source
http://www.nenie.org/misc/mpsys/
MPSYS: a MPEG2 system library and tools
https://www.videolan.org/vlc/index.pt.html
Vlc
http://mplayerhq.hu/
MPlayer
http://xine.sourceforge.net/ and http://xinehq.de/
Xine
http://www.mythtv.org/
MythTV - analog TV and digital TV PVR
http://dvbsnoop.sourceforge.net/
DVB sniffer program to monitor, analyze, debug, dump
or view dvb/mpeg/dsm-cc/mhp stream information (TS,
PES, SECTION)
4. Can't get a signal tuned correctly
That could be due to a lot of problems. On my personal experience,
usually TV cards need stronger signals than TV sets, and are more
sensitive to noise. So, perhaps you just need a better antenna or
cabling. Yet, it could also be some hardware or driver issue.
For example, if you are using a Technotrend/Hauppauge DVB-C card
*without* analog module, you might have to use module parameter
adac=-1 (dvb-ttpci.o).
Please see the FAQ page at linuxtv.org, as it could contain some
valuable information:
https://www.linuxtv.org/wiki/index.php/FAQ_%26_Troubleshooting
If that doesn't work, check at the linux-media ML archives, to
see if someone else had a similar problem with your hardware
and/or digital TV service provider:
https://lore.kernel.org/linux-media/
If none of this works, you can try sending an e-mail to the
linux-media ML and see if someone else could shed some light.
The e-mail is linux-media AT vger.kernel.org.
5. The dvb_net device doesn't give me any packets at all
Run ``tcpdump`` on the ``dvb0_0`` interface. This sets the interface
into promiscuous mode so it accepts any packets from the PID
you have configured with the ``dvbnet`` utility. Check if there
are any packets with the IP addr and MAC addr you have
configured with ``ifconfig`` or with ``ip addr``.
If ``tcpdump`` doesn't give you any output, check the statistics
which ``ifconfig`` or ``netstat -ni`` outputs. (Note: If the MAC
address is wrong, ``dvb_net`` won't get any input; thus you have to
run ``tcpdump`` before checking the statistics.) If there are no
packets at all then maybe the PID is wrong. If there are error packets,
then either the PID is wrong or the stream does not conform to
the MPE standard (EN 301 192, http://www.etsi.org/). You can
use e.g. ``dvbsnoop`` for debugging.
6. The ``dvb_net`` device doesn't give me any multicast packets
Check your routes if they include the multicast address range.
Additionally make sure that "source validation by reversed path
lookup" is disabled::
$ "echo 0 > /proc/sys/net/ipv4/conf/dvb0/rp_filter"
7. What are all those modules that need to be loaded?
In order to make it more flexible and support different hardware
combinations, the media subsystem is written on a modular way.
So, besides the Digital TV hardware module for the main chipset,
it also needs to load a frontend driver, plus the Digital TV
core. If the board also has remote controller, it will also
need the remote controller core and the remote controller tables.
The same happens if the board has support for analog TV: the
core support for video4linux need to be loaded.
The actual module names are Linux-kernel version specific, as,
from time to time, things change, in order to make the media
support more flexible.
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