[mythtv-users] [OT] Trancoding 'live'

glen martin glenm at locutory.org
Mon Dec 5 11:28:57 EST 2005

Michael T. Dean wrote:

> Chris Ribe wrote:
>> I think that is actually the roundtrip Glen is worried about.  He
>> would like to capture ATSC HD content and downconvert  it for an NTSC
>> display, thus keeping the signal digital until the final output for
>> display.
> Right.  It's "the exact same roundtrip."  I'm just pointing out that
> he may have already seen it if he had previously set up a
> cable/satellite receiver with Myth--even if he didn't realize he was
> seeing it in that context.  If he has seen it, he will know what to
> expect.

Right. I have DirecTV feeding Tivo as the main system for the family
while I get all the setup and config bugs out of a myth setup and get it
down to the level of repeatability the family needs. I never quite
realized how much loss there is in the signal quality, even on what is
referred to as 'Best' quality. DirecTV, or Tivo, or the loop between, is
trashing the signal.

Then my DirecTV receiver fried and I bought a new one (used) on ebay.
Because of my general musings about HD, I wound up buying an
OTA-HD/DirecTV STB (an old Zenith that is out of manufacture), mostly so
I could see what signals I could pick up from my house, which is 25
miles and two intervening hills away from the transmitter. Surprise
surprise, I could pick up signals just fine, and (here's the rub) the
picture quality blew me away. Put the STB on <ch#>-1 with 480i output
cropped to 4:3, plug it into my TV, and the picture was very noticeably
sharper than DirecTV->Tivo->TV for the same broadcast on a good 32"
flatscreen TV. Even for sports broadcasts, which DirecTV purportedly
encodes at a higher hit rate.

For completeness, I guess I really should be doing a more systematic
comparison to see whether it is DirecTV or Tivo that is causing the
problem. Or just the combination. But in reality, it is a bit moot. The
Tivo box must be getting near EOL.

So yes, I've seen the same problem in another pair of components, and
had hoped to find a (digital) ATSC->(digital)MythTV->headend and only go
analog as it is output to the NTSC TV.

Someone asked: how much do I record a day. Not a lot, usually. And most
of it is NTSC or SD. Only the occasional HD, and that is only OTA. So
slow transcoding after program complete is probably ok for the majority
of our viewing. It was only the very occasional live HD broadcast that I
cared to try to handle with realtime transcoding.

BTW, the fact that I actually own a standalone ATSC receiver made the
suggestion earlier in this thread that I connect such a box to the
PVR-*50 quite amusing. Or bemusing (he said, shaking his head). I had a
mental block on this because I was fixating on the digital signal
throughout. I'll really have to try this to see just how much of an
issue the analog loop is going to create.

- glen

> Mike
>> On 12/4/05, *Michael T. Dean* <mtdean at thirdcontact.com
>> <mailto:mtdean at thirdcontact.com>> wrote:
>>     glen martin wrote:
>>     >glen martin wrote:
>>     >
>>     >>Michael T. Dean wrote:
>>     >>
>>     >>
>>     >>My front-end can't support HD playback, and my TV can't display
>>     it. But
>>     >>I like the aspect ratio and extra channels (eg. 5 subchannels on
>>     PBS) of
>>     >>ATSC.
>>     >>
>>     >>>your best option for "live" transcoding from ATSC -> NTSC is
>>     plugging
>>     >>>the S-Video/Composite out of your cable box into a PVR-x50.  If
>>     you're
>>     >>>using OTA instead of cable, you could get a STB ATSC receiver
>>     (like
>> >>>http://www.bestbuy.com/site/olspage.jsp?skuId=7292146&type=product&productCategoryId=cat03022&id=1118840815760
>> <http://www.bestbuy.com/site/olspage.jsp?skuId=7292146&type=product&productCategoryId=cat03022&id=1118840815760>
>>     >>>-- note that I don't recommend this one as I've never used it,
>> but
>>     >>>it's the type of thing you would need).
>>     >>>
>>     >>That's an approach I hadn't considered. So for OTA use, I could
>> get
>>     >>something like this standalone ATSC receiver, set it for 480i
>>     output,
>>     >>feed that into a PVR-250 through the s-video input, and use
>>     MythTV as
>>     >>usual including pause etc. Interesting. I had a mental block on
>>     that,
>>     >>but seems obvious once you suggest it.
>>     >>
>>     >The only downside seems to be a roundtrip through analog between
>> the
>>     >external box and the PVR-250.
>>     >
>>     >
>>     Believe it or not, it's the exact same roundtrip you get with a
>>     Digital
>>     Cable/Satellite STB...  Just don't tell anyone or we might have a
>>     lot of
>>     people starting to notice "artifacts" from the D/A -> A/D -> D/A
>> (and
>>     add in an A/D before the process if the network feed to the
>>     cable/satellite company is analog instead of digital) process they
>>     didn't realize they were using.  :)
>>     Mike 

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