[mythtv-users] channel scan missing channels

Steven Adeff adeffs.mythtv at gmail.com
Sun Dec 19 23:24:03 UTC 2010

On Wed, Dec 15, 2010 at 11:33 AM, Steven Adeff <adeffs.mythtv at gmail.com> wrote:
> On Tue, Dec 14, 2010 at 7:56 PM, Michael T. Dean
> <mtdean at thirdcontact.com> wrote:
>>  On 12/14/2010 06:06 PM, Steven Adeff wrote:
>>> On Tue, Dec 14, 2010 at 3:06 PM, Michael T. Dean wrote:
>>>>  On 12/14/2010 01:50 PM, Steven Adeff wrote:
>>>>>>>  On 12/13/2010 04:54 PM, Steven Adeff wrote:
>>>>>>>> In doing a channel scan on my parents new mythbackend we've noticed
>>>>>>>> that Myth isn't finding all the channels that we find using the
>>>>>>>> digital tuner in their HDTV. I've done full scans of "Cable", "Cable
>>>>>>>> IRC" and "Cable HRC" at QAM-64, 128 and 256. I just can't seem to get
>>>>>>>> Myth to see the channels. I need to try to create the channel by hand
>>>>>>>> to see if Myth can tune them, but I'm wondering if anyone else has
>>>>>>>> run
>>>>>>>> into this before?
>>>>> anyone have any ideas? there's a few channel's Myth just won't find
>>>>> that the digital tuners they have *do* find, and they are HD channels
>>>>> so it would be nice if I could get Myth to tune them.
>>>> Have you tried to see if any other application using the exact same
>>>> hardware
>>>> (the PC and the PC tuners) can find them?  Something like dvbscan?
>>>>  http://www.mythtv.org/wiki/Dvbscan
>>>> Could well be tuner sensitivity/interference, etc., so we need to prove
>>>> that
>>>> it's actually the software--meaning we need to see some other software
>>>> that
>>>> uses the same hardware find those channels.
>>> I have tried other channel scanners, the problem is, none of them give
>>> me a usable output since they just show frequencies and sub channels,
>>> but not the "virtual" channel shown by Myth or the TV's digital tuner.
>>> On top of that, the mplexid value, which is basically the "channel" to
>>> the service value's sub channel is not the number shown as the channel
>>> on the digital tuner. So it makes it basically impossible to figure
>>> out how to use something like dvbscan/scan to manipulate Myth's
>>> channel database.
>>> here's the output from scan,
>>> http://www.mythtv.org/wiki/Westchester,_CA
>>> I created the link so as I figure out what channels are what I can put
>>> them there and hopefully help any others in that area.
>>> I've tried scanning multiple times, but there are just certain channel
>>> frequencies that Myth doesn't find/add.
>>> The cable line has plenty of signal strength and a strong S/N ratio.
>>> One of the digital tuners doing the scanning uses an output from the
>>> same splitter that goes to Myth (for the time being as we set Myth up)
>>> and has no trouble finding these channels.
>>> And Robert, yes, thank you for your channel scanner work, along with
>>> whomever helped. I remember trying to add QAM channels to Myth
>>> compared to doing things the old manual way 4 or 5 years ago, and it
>>> was not fun. I recently had to rescan my channels due to Comcast
>>> moving things around and I was up and running almost immediately with
>>> a proper channel mapping. I just wish Time Warner where my parents
>>> are, and whom this is for, was as easy...
>> So what specifically is missing from MythTV?
>> Mike
> Myth found about 80% of the channels that two digital tuners in the
> house found on a scan. There are two types of missing (sub)channels,
> 1) some sub channels are missing while others were found, all on the
> main channel. For instance, one channel/frequency has 8 sub channels
> (standard definition but digital), the TV's found all 8, Myth only
> found 5.
> 2) Some channels/frequencies only have one or two sub channels, the tv
> digital tuners found them, and Myth found none of them.
> for the first case I created my own channels by copying other channel
> entries on the main channel and just changing the sub channel. I don't
> know if this will work.
> Also, since the channel database mplexid entry (for the main
> channel/frequency) does not correspond with the main channel number
> used by the digital tuners and by Myth when it does find them, it
> makes things difficult/confusing. Since I don't know where the
> database holds the relation between the mplexid value, the channel
> number, and the channel frequency I can't easily "create" my own
> channels to see if they work. If the mplexid value matched the main
> channel number it would be great, ie. for channel 77-5, mplexid does
> not equal 77, but serviceid always equals 5, or 68-398, mplexid!=68,
> serviceid=398.
> My dad was able to get the VCTID from the cable box, so I'm running a
> new scan with scte65scan to see if it can find any channel info,
> perhaps even find the "missing" channels.
> I hope this explains a little better what's going on here.
> Thanks for the help all! I keep telling my parents Myth runs great in
> my house, they'll never believe me till I get theirs running as
> well...

Just spent a few hours on the phone with my dad going through using
the silicon dust listing and what he obtained from his HDTV digital
tuner and manually added the channels Myth's scan missed. They all
added fine, once I figured out the location of the mplexid table,

I'd still be willing to do some testing etc, as to why Myth missed the
channels in it's scan, but unless a dev tells me now to create a
ticket about this issue I won't bring it up again.

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