[mythtv] HDTV doc diff for channel settings

Brandon Beattie brandon+myth at linuxis.us
Wed Jul 21 15:19:25 EDT 2004

I agree we should not limit saying HDTV starts at 14, for now we should
probably say 2 to not prevent anything missing out.  I do want to note
that the maker of the pcHDTV wrote the channel detecter to start at 14,
I'll ping them about fixing that too.  Before you mentioned that you
received on a sub-14 channel, I didn't think that was possible.

Everyone, including most station techs, are learning about HDTV and some
probably know less than they should.  I think that would be good to
spread the word where we can about having things done the best/correct.
I guess my area is just bad at breaking rules. :)  If you're curious, I
can send you a dump of all my dtvstream scans so you can see how almost
every station is doing things differently.  One weekend I might get
board and let stations know if they're using PID 1 for audio/video.


On Wed, Jul 21, 2004 at 12:52:00PM -0400, Daniel Thor Kristjansson wrote:
> Look, there is HDTV transmitted on a VHF channel. Nothing physically
> prevents it, the bandwidth is still 6 Mhz in VHF. And, obviously the FCC
> allows it. It may be temporary, they are building a new radio tower, but
> it's there and someone might be confused if we tell them it doesn't
> exist.
> As for program id 1... I believe the station tech was talking about
> subchannels. Subchannel 0 is for NTSC, subchannel 1 is for primary
> service (usually HDTV), and any other subchannels are for secondary
> service, terciary service, etc. Using a pid of 1 is not recommended for
> any service, it's not because ATSC defines any use for that pid, but
> because much ATSC equipment is actually DVB equipment with a new label,
> and DVB defines a use for that pid. You will also never see a PID of 0
> because that is reserved for an MPEG-2 table, which ATSC is also tries
> to be compatible with.
> -- Daniel
> On Wed, 21 Jul 2004, Brandon Beattie wrote:
> ]The lowest I have seen is 29.  I did some quick math, UHF frequency for
> ]14-69 channels is 470-806 Mhz.  This is about 6.1Mhz per channel.  If
> ]you take 14 channels worth below 470 it's about 395, which is still
> ]higher than channels 7-13 VHF (174-216 Mhz) and channels 2-6 (54-88
> ]Mhz).  But below 470 is used for other /critical/ technologies.
> ]225-400Mhz is used for ATC/military communication, landing
> ]systems, and other general aviation transmissions.  400-406 is for US
> ]Goverment usages (Undefined).  420-450 is for Ham radio.  And 450-470 is
> ]used for military, fire, "local" goverment, and "businesses".  If you
> ]are getting channels 13, or below, the broadcaster is sending over radio
> ]frequencies that are for other purposes, which may be fine, I can't find
> ]any information detailing regulations on 395-470 for what would be HDTV
> ]channels 1-14.
> ]
> ]For the second item, that may be true.  The station tech I spoke with
> ]just said he came from the east coast and everyone out there basically
> ]said you should only use program ID 1 for the main HD channel and if you
> ]are only doing standard def the acceptable thing was to use program id 2
> ]instead, and reserve 1 for when they go HD.  All my stations out here
> ]also follow what he said with the exception of 1 that's using program ID
> ]1 for standard def, and 3 that don't have anything on program ID 1 and
> ]are broadcasting in standard def on program id 2.  The sad thing is it
> ]appears that there is no standard that everyone will probably agree on
> ]and follow.  Using id 1 for station information sounds really good, but
> ]I don't see anyone out here following that.  The one station that
> ]appears to have program information is running it on 34-7 here.
> ]
> ]--Brandon
> ]
> ]
> ]
> ]On Tue, Jul 20, 2004 at 10:28:28PM -0400, Daniel Thor Kristjansson wrote:
> ]>
> ]> This is a great improvement. But a couple nitpicks...
> ]>
> ]> * The frequency part of the "freqid" can be any channel starting at 2,
> ]>   in my city there are a couple ATSC stations on channel 12.
> ]>
> ]> * It is recommended to the broadcasters that they don't change the
> ]>   program id's often and that they never use program id 1. This is for
> ]>   faster tuning, and for compatability with DVB which uses program id 1
> ]>   for the Network Information Table. If you are using a freqid such as
> ]>   "44-1" and it works, this is only because MythTV tries to guess at the
> ]>   program id if you got it wrong, and often guesses correctly.
> ]>
> ]> -- Daniel
> ]>
> ]> On Tue, 20 Jul 2004, Brandon Beattie wrote:
> ]>
> ]> ]2 additions.
> ]> ]
> ]> ]I added one paragraph regarding what CPU is recommended for systems with
> ]> ]multiple HDTV tuners.  I've had so many problems with watching HDTV when
> ]> ]myth is trying to commercial detect more than one or two shows at a
> ]> ]time (Commercial detect set to low CPU).  A 2.4Ghz box may work just
> ]> ]fine for viewing live HDTV or previously recorded, but if you drop even
> ]> ]2 HDTV tuners and have more than 1 or 2 shows to commercial flag a 2.4Ghz
> ]> ]system is not going to cut it.
> ]> ]
> ]> ]The other addition is regarding how to setup myth for subchannels with
> ]> ]HDTV.  Examples, links to dtvstream, and explanation on how things work.
> ]> ]
> ]> ]I did change the sgml file, but I didn't add anything more than <sectx>
> ]> ]tags, someone who knows sgml may want to beautify my technical jabber.
> ]> ]
> ]> ]--Brandon
> ]> ]
> ]
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> ]
> ]

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