Tzap

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Revision as of 05:33, 24 April 2006 by Kkuphal (talk | contribs) (Dvb Apps 2ftzap moved to Tzap: Proper title)

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tzap

tzap is an essential utility for testing the tuning and streaming of your DVB adapter.

I'm assuming that the same applies to czap and szap (the cable and satellite variants of this util).

Usage

tzap requires you to have first placed a channels.conf file from [[../dvbscan]] into your ~/.tzap folder.

If you have a single DVB device, usage is as simple as

tzap "BBC ONE"

.. look inside your channels.conf for valid channels.

The output looks like this

using '/dev/dvb/adapter0/frontend0' and '/dev/dvb/adapter0/demux0'
reading channels from file '/root/.tzap/channels.conf'
tuning to 754166670 Hz
video pid 0x0258, audio pid 0x0259
status 00 | signal ffff | snr c000 | ber 00003fff | unc 00000000 |
status 01 | signal 3737 | snr c000 | ber 00003fff | unc 00000000 |
status 1f | signal 3636 | snr ffff | ber 00000000 | unc 00000000 | FE_HAS_LOCK
status 1f | signal 3636 | snr ffff | ber 00000000 | unc 00000000 | FE_HAS_LOCK
status 1f | signal 3636 | snr ffff | ber 00000000 | unc 00000000 | FE_HAS_LOCK
status 1f | signal 3636 | snr ffff | ber 00000000 | unc 00000000 | FE_HAS_LOCK

The "FE_HAS_LOCK" (frontend has lock) messages being the important indicator that your card has locked onto a signal. The other values are important diagnostic indicators.

The short explanation : frontends seem to vary in the way they present these numbers, it seems, so don't break your back trying to get the numbers "perfect". If the snr value is steady and reasonably high, and you can get a consistent lock, your card will probably work.

Testing with cat

You can use the tzap utility to record video. It's very primitive, but it works.

First, in one tty, set tzap going on the channel of your choice

tzap -r "BBC ONE"

The -r is the bit that makes it work. Now leave it running, go to another tty, and

cat /dev/dvb/adapter0/dvr0 > testvideo.mpg

The file should rapidly fill up with data. If it stays empty, something's not right.

Even better, you should be able to play this file through mplayer as simply as

mplayer testvideo.mpg

Interpreting the numbers

signal

This value is pretty self explanatory ; it's not actually all that important though. It's also rather misleading as different frontends report different values. My Nova-T reports ffff (100%), but it's being fed by the same signal as my DEC2000-t, which reports 6f45 (43%). Even more confusing, the DEC2000-t reports 84% signal when it's in STB mode.

snr

I've found that the signal/noise ratio is the most important indicator of your card working successfully. It doesn't need to be as high as possible (but higher values are better), but it seems it does need to be steady. My DEC consistently reports a SNR of 8004 (but the STB GUI reports signal quality of 100%). I was trying a poor antenna and I could get a signal on my Nova-T, even with a very poor signal strength, as long as the snr value was steady. Fluctuations in this value are bad news.

ber

The bit error rate presumably displays the error rate for the card. Again, while my Nova-t was reporting an error rate of zero, my DEC2000-t was reporting bffff8b8, despite the GUI on the box reporting 100% signal quality. Again, I think it's more important for this value to be steady than it is for it to be low.

unc

This value reports the number of uncorrected blocks. Low is good. Again, my DEC is producing misleading values here, so steady is as good as low, I think.