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

[Jarod C. Wilson]

On Tuesday, Sep 16, 2003, at 21:03 US/Pacific, Brandon Beattie wrote:

>>> I
>>> believe that saving a single stream is possible and could be very
>>> beneficial from within software, It would be nice to see a stream
>>> selection when HDTV really gets going so we can drop the lower 
>>> quality
>>> stream in transit(and vice versa) and just save the one we want, thus
>>> saving LOTS of hd space.
>>
>> My understanding is that you actually can do this with the pcHDTV. Or
>> at least, you can choose not to capture the unwanted audio streams 
>> that
>> are usually muxed in (i.e. SAP). I'm not certain about multiple
>> resolutions of HDTV streams. Is it your understanding that there
>> multiple HDTV resolutions broadcast for each HD channel? I thought it
>> was just one, and any down-sampling was done at the client end... Or
>> did I misunderstand what you were saying?
>
> An ATSC signal is up to 40Mb/s of data.  It can be used for almost
> anything (Audio or video mpeg2).  It's an mpeg2-ts stream, meaning it's
> a transport stream of an mpeg2 file that has built in redundancy for
> packet loss.  In the 40Mb/s ATSC signal, you can have X number of video
> streams and X number of audio streams _in the same channel space_.  In
> my area, 4 stations broadcast only 1 HD channel and 1 audio channel.

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!

> 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...

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...

> NBC and CBS both broadcast SD and HD versions of the same program
> schedule at once, and ABC shows their HD broadcast an hour before teir
> SD broadcasts/program schedules.  (And causes me to often record the
> wrong show.. (No HD broadcast listings availible yet for Myth)

D'oh!

> This should clear things up a bit.

Yes and no! I'm still kind of muddled on a few things...

>>> Transcoding is yet another thing and is rife
>>> with all it's own problems, but the newer transcode engine seems to
>>> handle
>>> everything now (last spring it didn't)...
>>
>> I'm curious to see how long it'll take to transcode a one-hour HD
>> show...
>
> 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?

--Jarod

-- 
Jarod C. Wilson, RHCE

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