[mythtv-users] OT: ATSC/QAM Encode to distribute HD over longer runs.

[Roger Heflin]

Chris Ribe wrote:
>> Depends.   It is trivial to do software encoding of menus into an atsc
>> stream to
>> provide menus and such,
> 
> 
> How do you figure?  Menus may be less computationally intensive to encode
> than other full motion video - but they still need to be full motion video.
> 

Not really, if the menu does not change, you have a keyframe, and then the the 
other difference frames that aren't anything, then generate a new keyframe when 
it changes again, no changes should mean you reuse the same keyframe and diff 
frames again with any other data that needs to be changed being changed to make 
it a proper data stream.

> 
> 
>>  most of the ATSC stream would be fed
>> directly (with no software decode/reencoding needed)
> 
> 
> What gets recorded to your harddrive when you record OTA DTV in Myth is not
> an entire ATSC stream, it is just an MPEG-2 transport stream.  It lacks
> various meta data that a TV would require in order to tune the signal.
> 
> 
> Multiplexing a previously recorded MPEG-2 transport stream into an ATSC
> stream would certainly be less computationally intensive than encoding video
> into a compliant MPEG-2 stream, but the later problem can at least be
> accomplished today with existing free software tools.

I have read out the raw DTV streams and given that it appears to be well 
documented and that tools like mplayer will rip out single AV streams, it would 
not be that hard to put a stream back together.

I guess that comes to another thing, no reason why one would only have to put 1 
channel, one could (with the correct software) multiplex a HD and a SD channel 
together, or multiple SD channels, though the software would get more 
complicated to do that, just like the TV stations do.

> 
> 
> 
>> And so far the "cheap" set top box (that does actual HD w/enet) is
>> $200-$300 and
>> you need one for *EACH* television, and if you have a number of TV's that
>> gets
>> to be more expensive than the other solution.
> 
> 
> This is true, but it would be much more difficult to provide multiple
> streams from a single backend if you were feeding ATSC streams.  Without the
> ability to have independent frontends, such a system would be of limited
> appeal.  Also, consider that very few TVs have multiple ATSC tuners, so you
> would need to work around the problem of still allowing those TVs to watch
> off ait TV.

I don't think the backend problem is that big anymore, a single 2+ Ghz quad core 
Intel should be able to handle at least 2 streams by itself, and maybe 3-4 
streams even encoding a fair amount of it.

Why would you need multiple tuners in the TV?  If you are running your house 
system, you modulate it onto a dead channel at your house's amp (in some cases 
you may need to have a notch filter to make some dead channel(s)), this is how 
people currently do it with NTSC (I have 2 house channels), the modulator 
becomes a 8VSB modulator rather than the older NTSC modulator, but you put it 
into a already dead channel, or you make a dead channel.

                                     Roger