Testing your DVB device

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This page provides a few suggestions on how to test that a DVB card installed on your system is functioning properly. It won't tell you how to install the specific hardware that you have (see the other pages of this wiki for that). Nor does this page describe the use of feature rich viewing software. But it will describe to you some steps on the command line that are indispensable for quick setup and viewing with DVB hardware.

Again, this article assumes that you have already physically installed the device into your system, and have also installed the driver for your hardware and have the proper modules loaded i.e. if you have, then you should have a non empty


directory. N will equal 0 if you have only one device installed on your system, otherwise, devices will be assigned a number accordingly. See 'HOW to Install a DVB Device' for some generic instructions for the configuration of DVB device hardware and modules on a system.

First step using dvb-utils - create a channels.conf file

The dvb-utils have many useful tools with great functionality. To install it on a debian system:

 # apt-get install dvb-utils

With gentoo:

 # emerge linuxtv-dvb-apps

The first step is to scan for the channels you can receive. Depending on where you get your dvb-utils package, the program to use is called 'scan', 'scandvb' or 'dvbscan'. In the following examples, we'll use the name 'scan'.

Scan will need some idea of where to start searching; for this reasons it takes a file for your location as a starting point. Therefore, you need to find channel information for your locality. Again, the location where they are installed may vary. In the following examples, the directory is /usr/share/doc/dvb-utils/examples/scan/dvb-t/; other installations also use /usr/share/doc/dvb-apps-1.1.1 or /usr/local/share/dvb/scan/dvb-t/. DVB-S users should use the folders /usr/share/doc/dvb-utils/examples/scan/dvb-s/, /usr/share/doc/dvb-apps-1.1.1 or /usr/local/share/dvb/scan/dvb-s/. In each case, the name of the file you're looking for is of the form cc-Ttttt, where cc is a two-letter country abbreviation, and Ttttt is the name of the location of the transmitter. So in Adelaide, Australia, you'd look for a file called au-Adelaide; the following example relates to Oxford in the United Kingdom.

NB: In recent distributions of dvb-utils the "scan" program has been replaced by "scandvb"

For the beginning, do something like this: Adopt this line for your place

 scan /usr/share/doc/dvb-utils/examples/scan/dvb-t/uk-Oxford 

and you'll see what's coming in to the card. If that makes sense, repeat it like this:

 mkdir /root/.tzap
 scan /usr/share/doc/dvb-utils/examples/scan/dvb-t/uk-Oxford \
    > /root/.tzap/channels.conf

This tries to find the programs it takes from the initial uk-Oxford configuration (or whatever your place is). Note that the screen output you get into your shell doesn't really say if you can receive something or not. The file it creates is more important; it has lines like:


which says that the stream on frequency 578000000 Hz has the two PIDs 600 and 601 for the video and audio stream of BBC ONE. This file with the data for your TV-programs, if stored into the place as above, can be used by the zapper tzap, e.g.:

 tzap Bloomberg -- Bloomberg

That tunes automatically both channel and PIDs for video and audio to the channel called "Bloomberg -- Bloomberg". Use the command tzap for DVB-T. For DVB-C, replace tzap with czap and for DVB-S with szap. The output of tzap is something like

 using '/dev/dvb/adapter0/frontend0' and '/dev/dvb/adapter0/demux0'
 tuning to 778000000 Hz
 video pid 0x040f, audio pid 0x040e
 status 1f | signal 5100 | snr 6200 | ber 00000000 | unc 00000000 | FE_HAS_LOCK
 status 1f | signal 5100 | snr 6200 | ber 00000000 | unc 00000000 | FE_HAS_LOCK
 status 1f | signal 5100 | snr 6200 | ber 00000000 | unc 00000000 | FE_HAS_LOCK#
 (end it with Ctrl C)

Not all the numbers are implemented in some drivers, but good is signal > 8000, status 1f (all bits set), snr (Signal to Noise Ratio) should be > 8000, ber (bit error rate) - low is good, unc (Uncorrectable blocks) - low is good.

You could now start up your TV watching application or datastreamer. But we want to see some nice statistics of what's coming in for each channel and PID:


And finally


Note: if your signal is too weak and you receive only some channels, the way to find out which is to look in the channel.conf file that you just created. If for a program the two PIDs (third and second last number in line) are 0, you can't receive it. If the first PID is 0 and the second is not 0, then it's probably a radio channel.

First steps using DVBtools - create a channels.conf (USA OTA Fedora azap example)

This is adapted from the above UK example showing the use of dvb tools in an installation of Fedora Core 6 2.6.19-1.2895.fc6 using an Air2pc HD5000av PCI dvb board receiving OTA (Over the Air) 8VSB signals in the USA. (Feb 2007)

Using Fedora, assume root privileges then install the dvb utilities with

  # yum install dvb-apps

First try

 $ /usr/bin/scandvb /usr/share/dvb-apps/atsc/us-ATSC-center-frequencies-8VSB

This should produce output saying "WARNING: >>> tuning failed!!!" if a signal was not found on that particular frequency. Eventually, a list of services found should be displayed. Here is a sample list:

 dumping lists (7 services)

Note that if you are attempting to decode us cable-tv QAM from your cable set top box, you might use the file /usr/share/dvb-apps/atsc/us-Cable-Standard-center-frequencies-QAM256 rather than /usr/share/dvb-apps/atsc/us-ATSC-center-frequencies-8VSB

Next try to create a "channels.conf", a file in a hidden (dotted) directory off your "home" directory.

 $ mkdir ~/.azap
 $ scandvb /usr/share/dvb-apps/atsc/us-ATSC-center-frequencies-8VSB > ~/.azap/channels.conf

Next display the contents of the channels.conf file to make sure the file creation proceeded correctly

 $ cat ~/.azap/channels.conf

Note: For reasons not readily apparent, tzap used in the UK example above didn't work. So try azap instead, picking the first entry from ~/.azap/channels.conf (The KPAX-DT part)

 $ /usr/bin/azap  -r -c ~/.azap/channels.conf "KPAX-DT"

which in turn displays lines similar to (terminate with Ctrl-C)

 using '/dev/dvb/adapter0/frontend0' and '/dev/dvb/adapter0/demux0'
 tuning to 177028615 Hz
 status 1f | signal 0000 | snr ff28 | ber 00000000 | unc 00000000 | FE_HAS_LOCK
 ... (repeated output) ...

Then for some statistics, try

 $ /usr/bin/dvbtraffic

First steps using dvbsnoop

As an alternative, dvbsnoop is a small, down-to-earth util. As it's very hardware-near, it's very handy for debugging and seeing what's going on with the card (tuning works? data coming in? signal strong enough?). (On the other side, if all in the section above works fine, you can jump over this section here.) Install it, e.g. with debian:

 # apt-get install dvbsnoop

Apparently, dvbsnoop isn't in any of the usual Fedora repositories at this time (Feb 2007). Instead, download a copy directly from the source forge site using steps similar to the following. Note this is for version 1.40. Your download URL (and the extracted directory dvbsnoop-bin-i386-1.4.00-api3) will change as succeeding versions of dvbsnoop are published on Source Forge. Also you may wish to copy the binary dvbsnoop out to a more convenient directory in your path, rather than the deeply buried directory ~/dvbsnoop/dvbsnoop-bin-i386-1.4.00-api3/bin-i386-api3 which, in this example, contains the binary. Then ./dvbsnoop will not be required, just dvbsnoop as shown in the debian example below.

 $ mkdir ~/dvbsnoop
 $ cd dvbsnoop
 $ wget  http://downloads.sourceforge.net/dvbsnoop/dvbsnoop-bin-i386-1.4.00-api3.tar.gz?modtime=1124046233&big_mirror=0
 $ tar xvzf *.tar.gz
 $ ls
 $ cd dvbsnoop-bin-i386-1.4.00-api3
 $ ls 
 $ cd bin-i386-api3
 $ ls
 $ ./dvbsnoop -help
 $ ./dvbsnoop -s pidscan

Then try things like

 dvbsnoop -help
 dvbsnoop -s pidscan

This will give out a lot of numbers, but if you understand the system of DVB you should see if they make sense. Go for one of the PIDs (choose a right one which is a bit difficult as you don't know what they stand for unless you used the scan line above) and try:

 dvbsnoop -s bandwidth <PID>
 dvbsnoop <PID>

The latter will spit out a lot of hexdumps - at least you receive something ;-)

Save a TV program to harddisk with dvbstream

The handy thing about digital TV is, it comes in as a digital stream that you can save right away to your harddisk without any changes necessary to it. Therefore, hardly any CPU resources are needed -- just a lot of HD space (few GB per hour as the stream is MPEG-2 which is not as compressed as for example DivX/MPEG-4). A good program that can do that (and more) is dvbstream.

Install it, e.g. with debian:

 # apt-get install dvbstream

Let's tune into a channel with tzap as described above, and then you can just save the stream into a file like this:

 tzap BBC ONE
 dvbstream 600 601 -o >BBC1.mpeg

So this is why it's important that you have your personal channels.conf file with all the PIDs so you can look them up. Instead of using tzap you can do it all in one - tune the frequency and select the right PIDs:

 dvbstream -f 578000 600 601 -o >bbc1.mpeg

Wait a few seconds and then press Ctrl+C to stop. You can open the MPEG file with players that play movie files (decode MPEG2), like mplayer, (g)xine or noatune.

If the file is rather small, e.g. smaller than 1 MB after a minute of recording, then you can't receive this TV channel - maybe the reception is bad (too weak antenna signal) - or maybe your card's frequency is not tuned for the right sender? Watch out, some PIDs come up a few times (but for different frequencies).

This might not be what you wanna do every day (unless you only watch BBC1 or you can easily memorise all your channels with their two PIDs) - but it's very fast and easy to do these steps, e.g. for a test.

More Software - next steps

You have a lot of choice. Mplayer, Xine, Kaffeine , Klear are probably the first choices selected for light TV watching with a DVB card.

Alternatively, you could use dvbstream and then watch the MPEG-2 stream (even possible on a different computer) with programs like xine, mplayer etc.

For "Media Center" type applications, the usual first suspects are Freevo, MythTV, and VDR (note: you'll need to install the VDR Software Decoder Plugin if you want to use VDR for watching with a software decoding card).

Also See