[mythtv-users] PCI-E ATSC (US) Card Recommendation

Brian Wood beww at beww.org
Tue Dec 1 17:22:10 UTC 2009

On Tuesday 01 December 2009 10:19:03 am Patrick Doyle wrote:
> On Tue, Dec 1, 2009 at 12:11 PM, Brian Wood <beww at beww.org> wrote:
> > On Tuesday 01 December 2009 09:52:42 am Devin Heitmueller wrote:
> >> Hi Brian,
> >>
> >> On Tue, Dec 1, 2009 at 11:47 AM, Brian Wood <beww at beww.org> 
> >> > I assume you mean "hardware NTSC decoders", unless the unit has
> >
> > NTSC
> >
> >> > outputs ???
> >>
> >> I think you just have the terminology backwards.  An MPEG encoder
> >> converts a raw NTSC signal to MPEG format.  An MPEG decoder 
> >> an MPEG file to raw video.  James is correct in that the 2250 has dual
> >> MPEG encoders.
> >>
> >> > Do you mean it can receive NTSC analog broadcasts (assuming 
> >> > drivers)?
> >>
> >> The hardware supports it, but the Linux driver does not.
> >
> > OK, makes sense. I thought that your reference to "NTSC encoders" 
> > mean that it could receive ATSC signals then output them as analog for
> > use by older NTSC TV sets or capture by a PVR-150. If that were the 
> > it would have been the first such unit I had heard of. Alas, that's not
> > the case.
> I was confused the first time I looked at some data sheets for
> composite video encoders and decoders.  For whatever reason (and I'm
> sure there are good hysterical reasons for this), a video "decoder"
> chip is one that locks onto the composite signal and extracts the Y,
> Cr, and Cb signals (and, for the ones I looked at for a job I was
> doing a few years ago) typically outputs a digitized stream to
> something like a DSP or an ASIC.  The video "encoder" chip would
> output an NTSC (or PAL) signal from the digital stream.
> It's completely backwards from what I typically think of when I hear
> MPEG-2 encoder and MPEG-2 decoder, but that appears to be the
> terminology in use.

An encoder takes something in and outputs MPEG, a decoder takes in MPEG 
and outputs something else.

If it wasn't confusing the engineers involved would be falling down on the job 

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