mythtv and digital tv

Ben Scott dragonhawk at gmail.com
Fri Jul 25 12:04:14 EDT 2008


On Fri, Jul 25, 2008 at 7:11 AM, Frank DiPrete <fdiprete at comcast.net> wrote:
>>  Encoding or decoding?
>
> Encoding on the backend where the card goes.

  If you're capturing digital TV (OTA or cable), no encoding is
needed.  The "stream" is already encoded, digitized, compressed,
folded, spindled, and mutilated.  This doesn't mean encoding is done
on the host CPU; it means there's no encoding to do, period.

  This is *why* there's a big push to switch over to digital TV, even
for standard definition channels.  Digital TV uses a lot less
bandwidth than analog NTSC, because it's compressed.  They can fit
something like six standard definition digital channels into the
bandwidth consumed by one NTSC analog channel.

  The only way the host CPU would be doing any encoding would be if
you wanted to transcode to a different format, e.g., for a player that
doesn't do MPEG, or something like that.

> 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.

-- Ben


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