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media: docs: update Digital TV faq.rst

Browse Source 
This file contains lots of obsoleted information. Update it
to reflect the current status and tools used by Digital TV
users and add pointers to the current locations and to
LinuxTV wiki pages.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
This commit is contained in:
Mauro Carvalho Chehab 2020-03-09 17:21:16 +01:00
parent fe877259d8
commit 8a1bfbc70d
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Documentation/admin-guide/media/faq.rst
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@ -5,101 +5,143 @@ FAQ
.. note::
This documentation is outdated. Please check at the DVB wiki
at https://linuxtv.org/wiki for more updated info.
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:
Some very frequently asked questions about linuxtv-dvb
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.o module parameter "dvb_shutdown_timeout"
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?
The driver distribution includes some simple utilities which
are mainly intended for testing and to demonstrate how the
DVB API works.
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:
Depending on whether you have a DVB-S, DVB-C or DVB-T card, use
apps/szap/szap, czap or tzap. You must supply a channel list
in ~/.[sct]zap/channels.conf. If you are lucky you can just copy
one of the supplied channel lists, or you can create a new one
by running apps/scan/scan. If you run scan on an unknown network
you might have to supply some start data in apps/scan/initial.h.
https://git.linuxtv.org/v4l-utils.git/
If you have a card with a built-in hardware MPEG-decoder the
drivers create a video4linux device (/dev/v4l/video0) which
you can use to watch TV with any v4l application. xawtv is known
to work. Note that you cannot change channels with xawtv, you
have to zap using [sct]zap. If you want a nice application for
TV watching and record/playback, have a look at VDR.
You can find more information at the LinuxTV wiki:
If your card does not have a hardware MPEG decoder you need
a software MPEG decoder. Mplayer or xine are known to work.
Newsflash: MythTV also has DVB support now.
Note: Only very recent versions of Mplayer and xine can decode.
MPEG2 transport streams (TS) directly. Then, run
'[sct]zap channelname -r' in one xterm, and keep it running,
and start 'mplayer - < /dev/dvb/adapter0/dvr0' or
'xine stdin://mpeg2 < /dev/dvb/adapter0/dvr0' in a second xterm.
That's all far from perfect, but it seems no one has written
a nice DVB application which includes a builtin software MPEG
decoder yet.
https://www.linuxtv.org/wiki/index.php/DVBv5_Tools
Newsflash: Newest xine directly supports DVB. Just copy your
channels.conf to ~/.xine and start 'xine dvb://', or select
the DVB button in the xine GUI. Channel switching works using the
numpad pgup/pgdown (NP9 / NP3) keys to scroll through the channel osd
menu and pressing numpad-enter to switch to the selected channel.
The first step is to get a list of services that are transmitted.
Note: Older versions of xine and mplayer understand MPEG program
streams (PS) only, and can be used in conjunction with the
ts2ps tool from the Metzler Brother's dvb-mpegtools package.
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:
3. Which other DVB applications exist?
https://www.linuxtv.org/wiki/index.php/Dvbv5-scan
http://www.cadsoft.de/people/kls/vdr/
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
http://www.metzlerbros.org/dvb/
Metzler Bros. DVB development; alternate drivers and
DVB utilities, include dvb-mpegtools and tuxzap.
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.linuxdvb.tv/
Henning Holtschneider's site with many interesting
links and docs
http://www.dbox2.info/
LinuxDVB on the dBox2
http://www.tuxbox.org/ and http://cvs.tuxbox.org/
http://www.tuxbox.org/
the TuxBox CVS many interesting DVB applications and the dBox2
DVB source
https://linuxtv.org/downloads
DVB Swiss Army Knife library and utilities
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
MPlayer
http://xine.sourceforge.net/ and http://xinehq.de/
xine
Xine
http://www.mythtv.org/
MythTV - analog TV PVR, but now with DVB support, too
(with software MPEG decode)
MythTV - analog TV and digital TV PVR
http://dvbsnoop.sourceforge.net/
DVB sniffer program to monitor, analyze, debug, dump
@ -108,62 +150,67 @@ Some very frequently asked questions about linuxtv-dvb
4. Can't get a signal tuned correctly
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).
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
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
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.
configured with ``ifconfig`` or with ``ip addr``.
If tcpdump doesn't give you any output, check the statistics
which ifconfig 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,
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.
use e.g. ``dvbsnoop`` for debugging.
6. The dvb_net device doesn't give me any multicast packets
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:
.. code-block:: none
lookup" is disabled::
$ "echo 0 > /proc/sys/net/ipv4/conf/dvb0/rp_filter"
7. What the hell are all those modules that need to be loaded?
7. What are all those modules that need to be loaded?
For a dvb-ttpci av7110 based full-featured card the following
modules are loaded:
In order to make it more flexible and support different hardware
combinations, the media subsystem is written on a modular way.
- videodev: Video4Linux core module. This is the base module that
gives you access to the "analog" tv picture of the av7110 mpeg2
decoder.
- v4l2-common: common functions for Video4Linux-2 drivers
- v4l1-compat: backward compatibility layer for Video4Linux-1 legacy
applications
- dvb-core: DVB core module. This provides you with the
/dev/dvb/adapter entries
- saa7146: SAA7146 core driver. This is need to access any SAA7146
based card in your system.
- saa7146_vv: SAA7146 video and vbi functions. These are only needed
for full-featured cards.
- videobuf-dma-sg: capture helper module for the saa7146_vv driver. This
one is responsible to handle capture buffers.
- dvb-ttpci: The main driver for AV7110 based, full-featured
DVB-S/C/T cards
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.