[mythtv] HDTV doc diff for channel settings
Daniel Thor Kristjansson
danielk at cat.nyu.edu
Wed Jul 21 12:52:00 EDT 2004
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
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.
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
]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.
]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.
]> mythtv-dev mailing list
]> mythtv-dev at mythtv.org
More information about the mythtv-dev