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Some very frequently asked questions about linuxtv-dvb
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"
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.
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.
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.
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.
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.
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.
3. Which other DVB applications exist?
Klaus Schmidinger's Video Disk Recorder
Metzler Bros. DVB development; alternate drivers and
DVB utilities, include dvb-mpegtools and tuxzap.
Dave Chapman's dvbtools package, including
dvbstream and dvbtune
Henning Holtschneider's site with many interesting
links and docs
LinuxDVB on the dBox2
the TuxBox CVS many interesting DVB applications and the dBox2
DVB source
DVB Swiss Army Knife library and utilities
MPSYS: a MPEG2 system library and tools
MythTV - analog TV PVR, but now with DVB support, too
(with software MPEG decode)
DVB sniffer program to monitor, analyze, debug, dump
or view dvb/mpeg/dsm-cc/mhp stream information (TS,
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).
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.
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,
then either the PID is wrong or the stream does not conform to
the MPE standard (EN 301 192, 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 the hell are all those modules that need to be loaded?
For a dvb-ttpci av7110 based full-featured card the following
modules are loaded:
- videodev: Video4Linux core module. This is the base module that
gives you access to the "analog" tv picture of the av7110 mpeg2
- v4l2-common: common functions for Video4Linux-2 drivers
- v4l1-compat: backward compatibility layer for Video4Linux-1 legacy
- 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