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