mythtv and digital tv
Derek Atkins
warlord at MIT.EDU
Fri Jul 25 12:20:49 EDT 2008
Quoting Ben Scott <dragonhawk at gmail.com>:
>> The goal is to write mpeg2 files to the server for playback like the pvr-250
>> does via its encoder. I'd like to believe that the term "digital streams"
>> means mpg2/aac ...
>
> ATSC is MPEG-2 video and AC-3 audio. I've read digital cable is
> basically ATSC with different modulation and a few extra tweaks.
Correct. Cable uses QAM modulation (instead of VSB-8, which is what
gets used for over-the-air ATSC transmission). The data stream is
effectively the same as you'd get for over-the-air digital, MPEG-2
transport stream.
The biggest difference is that cable companies can choose to
encrypt their QAM, which means you either need a cablebox or a
device with a cablecard. As far as I know no device usable by
mythtv directly can use a cablecard without having yet another
Digital-Analog-Digital conversion.
So for example, for SD you could have mythtv control a cablebox and
then read it in via a PVR-250. For HD you could effectively do
the same but use an HD-PVR box. But if your cable company is
really nice (RCN no longer falls under this category) then they
don't encrypt your QAM and you could just plug an HD-Homerun
directly into your cable. *sighs*
> -- Ben
-derek
--
Derek Atkins, SB '93 MIT EE, SM '95 MIT Media Laboratory
Member, MIT Student Information Processing Board (SIPB)
URL: http://web.mit.edu/warlord/ PP-ASEL-IA N1NWH
warlord at MIT.EDU PGP key available
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