[mythtv] DVB radio stutters on playback

Daniel Kristjansson danielk at cuymedia.net
Thu Jan 24 22:18:23 UTC 2008


On Thu, 2008-01-24 at 12:58 +0000, Stuart Morgan wrote:
> On Thursday 24 January 2008 12:40:39 Ronald Frazier wrote:
> > > Audio only has been supported for a long time, originally by generating a
> > > dummy video stream.
> >
> > Is that for DVB only, or would it include QAM-256.
> 
> "QAM-256" as it's erroneously called, is DVB* or ATSC. What I can't tell you 
> is whether US cable broadcast their radio channels in a format MythTV 
> understands.
>
> *(Personal annoyance to me that US Cable operators have been selling their 
> digital product as "QAM-256", for a start its 256 QAM and secondly that's not 
> the data standard but the modulation.)

"QAM-256" is a US cable industry standard which employs "256 QAM"
modulation plus it adds a custom FEC layer on top and specifies
specific frequencies to use. Also US Cable broadcasters, for the most
part, employ neither the DVB nor ATSC standards but use their own
bastardized MPEG variant, with out-of-band signalling employing a
TDMA modulation scheme. Which is why MythTV can't pick up the
scheduling data, and can't pick up the channel names when scanning
a "QAM-256" Cable network. The info is all on the TDMA channel
which the hardware can't demodulate for us.+

-- Daniel

+ There is a spec for in-band PSIP similar to ATSC's PSIP,
  but I haven't seen it in the wild yet.




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