7. FAQ

Note

This documentation is outdated. Please check at the DVB wiki at https://linuxtv.org/wiki for more updated info.

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?

    http://www.cadsoft.de/people/kls/vdr/

    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.

    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/

    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

    http://mplayerhq.hu/

    mplayer

    http://xine.sourceforge.net/ and http://xinehq.de/

    xine

    http://www.mythtv.org/

    MythTV - analog TV PVR, but now with DVB support, too (with software MPEG decode)

    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

    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, 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"

  1. 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 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