[mythtv] dvb-t confusion

Kenneth Aafl°y lists at kenneth.aafloy.net
Thu Jul 8 17:29:31 EDT 2004


On Thursday 08 July 2004 22:12, Jukka Tastula wrote:
> Next I got back to the setup program and start the channel editor. Now on
> the first page, what is the "Channel number" actually used for? Is it just
> an identifier for the channel or is it used in tuning the channel?

What you enter with the remote during LiveTV?

> I select the tv format PAL as that seems to be the most likely candidate
> (does it even matter in dvb?) and got to the next page. Now here it seems
> that whatever I enter in "FEC" gets copied to "HP Coderate" and other way
> around, same for "modulation" and "constellation" .. is this intended or
> am I/the program doing something wrong? I understand FEC is only used for
> cable and not dvb-t.

They use the same field/storage space in the database, because they will never 
be used at the same time.

> but then I have this confusing channels.conf entry 
> that "scan" gives me and it says FEC_2_3:FEC_NONE ... so which one is it?
> Should I just leave all these settings at "auto"? I do know what the
> correct values for all the options are but these programs don't seem to be
> so sure which option is which.

I belive the order of a vdr channel.conf if coderate_hp:coderate_lp.

> Next page is the pids, I filled out for each channel the video, audio,
> teletext, subtitle and service id. This should be enough?

teletext and subtitles will screw with your setup and is not supported yet,
and I belive this is mention in the howto that is here (down today it seems):
http://www.ethics-gradient.net/myth

> Decided I was done with the setup program and started up mythfrontend and
> opened the setup menu. There in tv settings recording profiles I see a new
> entry: "Hardware DVB Encoders"... sounds good. It has all the same
> profiles as the analog card I had previously installed had. I open up the
> one titled "Live TV". Now I'm really confused because the "image size"
> page has settings for width and height??? What exactly are these for? Then
> when I enter the next page I'm even more confused as it's the exact same
> "video compression" page as for analogue cards. I can select a codec mpeg4
> or rtjpeg and bitrate etc ... What good are these for live tv when the
> card pushes out perfectly good mpeg2 already? Same for all the other
> recording profiles, none of them seem to let me just record the mpeg2 the
> card pushes out natively? If I'm supposed to ignore all these settings
> it's certainly not very clear.

I don't use it, but it is for transcoding, isn't it? LiveTV won't be affected 
by these settings then offcourse.

> Now when I selected live tv I got what I pretty much expected after all
> this guessing. A black screen. It stayed there, frozen for a few seconds,
> 10 maybe. Not a sound or frame came out of it during this time. So I look
> in the logs ...
>
> >02:23:00 Changing from None to WatchingLiveTV
> >02:23:00 DVB#0 Using DVB card 0, with frontend DST TERR.
>
> Looks like it actually knows what my card is.
>
> >02:23:00 DVB#0 WARNING - Unsupported code_rate_hp option.
> >02:23:00 DVB#0 WARNING - Unsupported constellation parameter.
>
> What are these two about? 2/3 should be very much legal value for HP
> Coderate and QAM 64 for constellation.

Your card/frontend does not support the options you entered in the channel 
configuration, they will default to auto.

> >02:23:00 DVB#0 Successfully tuned to channel .
>
> Too bad it does't tell me which frequency that is

Doesn't it do that with 'mythbackend -v channel' ?

> >02:23:00 DVB#0 Recorder: Card opened successfully.
> >02:23:00 DVB#0 WARNING - Uncorrectable error in packet, dropped.
> >02:23:00 DVB#0 WARNING - Uncorrectable error in packet, dropped.
[snip]
> After this I'm back at the tv menu.
>
> Now I figured these errors and continuity errors and packet drops are
> because of poor signal quality. Trying with tzap ; dvbstream |mplayer - I
> sure can see lots of errors again, lots and lots of errors but once in a
> while there's a few seconds or almost watchable video.
[snip]

I guess you should fix your reception as a first priority. If you tell your 
location and cardtype, maybe someone with the same DVB-T card could give you 
a pointer on high the card dependent signal/noise/strength settings should 
be. But I would guess 3/4th is something to aim for.

Kenneth


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