[mythtv-users] Is the pchdtv card looking good?

[Jarod C. Wilson]

On Wednesday, Sep 17, 2003, at 22:56 US/Pacific, Brandon Beattie wrote:

>> I guess I just thought one HD, one audio was the norm. Goes to show 
>> how
>> very little I know about HDTV. I bow to your HDTV knowledge!
>
> I bow to others, it's a great circle. :)

Heh. I bow to lots of folks... Primarily my wife, but... ;p

>>> Both PBS stations have a SD (standard def 720x480p) that is the same 
>>> as
>>> their NTSC broadcast and they also have a second audio and video
>>> (subchannel is what they are called) for HD broadcast that are almost
>>> always a different program schedule than that on the first 
>>> subchannel.
>>
>> Odd. PBS here (on Comcast cable, that is) has one NTSC channel, then
>> three distinct HD channels. I'm thinking the cable companies probably
>> want to limit how much bandwidth gets sucked up, and thus break things
>> out to different channels, and only one resolution each. Just
>> theorizing though...
>
> They could be doing that... never heard of it being done that way
> though.

Never heard of them sending only one rez and audio track, or never 
heard of them putting NTSC and HD on distinct channels (even when they 
are the same show)?

>> If multiple streams are on the same channel (HD and NTSC), how does 
>> one
>> pick out which to use? I'm assuming the receiving hardware just
>> auto-picks what it thinks is best... I really ought to spend some time
>> on the AVSForum site...
>
> No, tuners all you to select subchannels.  If I try to flip from 7.1
> (PBS NTSC station) to the "next channel up" a HD tuner would go to 7.2
> (PBS ATSC station).  It's the tuners job to change stations and then
> display whatever subchannel.  And in the case of this "channel change
> up" there is no change on frequency listening, it's just that it drops
> subchannel 1, and shows subchannel 2 (as before it was showing channel 
> 1
> and dropping subchannel 2)

Aha. This further leads me to believe Comcast breaks stuff up. ABC is 
channel 4, ABC-HD is channel 104. PBS is channel 9, PBS-HD is channles 
108, 109 & 110. ESPN is channel 30, ESPNHD is channel 173, etc, etc.

>>> To transcode from mpeg2-ts to mpeg2-ps (Ie, used for dvd's, and it 
>>> just
>>> has the erducdency taken off, and you can also strip off the unwanted
>>> subchannels if there are any) it takes a few minutes.  All you are
>>> doing
>>> is dropping off data from the current file mostly.
>>
>> So it isn't actually the pcHDTV card that drops the extra audio and
>> video channels, it is transcode that does this work?
>
> The pcHDTV card tunes to a frequency (ie, channel 7) you get all
> subchannels (7.1 and 7.2) at the same time.  Then in xine or mythtv
> (which are being used for the "tuner") it displays subchannel .1, or .2
> and ignores the other.  But if you use the dtvdump program on channel 
> 7,
> you get everything, 7.1, 7.2, all written to a single file.  Then it's
> up to a player (Xine, mplayer, mythtv) to have support to pick which
> subchannel to play in that stream/file.

So when you are capturing HD channels w/the pcHDTV in mythtv, is it 
using dtvdump for the actual capture, then picking out the subchannel 
to play back?

--Jarod

-- 
Jarod C. Wilson, RHCE

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