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Dual Stations (channels) with DVB card
http://forums.linhes.org/viewtopic.php?f=23&t=20761		 Page 1 of 1
Author:  bkamen [ Sun Jan 10, 2010 2:48 pm ]
Post subject:  Dual Stations (channels) with DVB card
I noticed in the DVB:0 (pcHDTV-3000) that it wants to set the number of "Max Recordings" to 2... it explains that some multi-DTV stations on a single Frequency can be recorded.

Has anyone tried this who can elaborate a little more how this works?

In theory, it makes sense to me, I'd just like to hear from someone who uses it in practice.

Thanks,

-Ben
Author:  Too Many Secrets [ Sun Jan 10, 2010 6:57 pm ]
Post subject: 
I use this feature as it enables me to record 'back to back' programs on the same channel with the same physical card. Before the 'back to back' scenario would require two actual encoders as the recordings would run over each other. Now mythtv 'sees' two encoders for the single physical encoder and allows the 'back to back' to happen smoothly.

There are other ways this can be useful when recording QAM digital stations, but my cable provider doesn't play nice in this area.
Author:  bkamen [ Sun Jan 10, 2010 7:46 pm ]
Post subject: 
I just played with this while recording something on 3-1 and watched something on 3-2. Myth will let me switch channels but limits me to 3-1 or 3-2.

That's pretty cool.

Nice to see it workin... Nifty indeed.

-Ben
Author:  tjc [ Sun Jan 10, 2010 8:01 pm ]
Post subject: 
It's funny how the same question will pop up several times in quick succession around here. I was just answering something very like this for kmkittre in this thread - http://knoppmyth.net/phpBB2/viewtopic.php?t=20756

Basically it works like this:

    - A single ATSC or QAM frequency is actually a multiplexed channel (translation - it has several signals combined together).

    - In the ATSC (OTA) world these are typically the sub-channels for a particular broadcaster, e.g here in eastern MA "WGBX44" @ 44.1, "WGBH World" @ 44.2, "WGBH Create" @ 44.3, and "WGBH Kids" @ 44.4 for the local PBS station's second frequency.

    - In the QAM (cable) world there may be as many as 10-12 sub-channels for a given frequency. Even more for the audio only channels with lower bandwidth requirements.

    - When your tuner is set to a particular frequency it's actually receiving all the streams and de-multiplexing (splitting) out just the one(s) you want.

    - Rather than discarding the extra streams, given the right software it's possible to treat them as extra virtual tuners.

    - Once you have that abstraction in place, It's even possible to clone the same stream and treat it as two separate streams. Thus using one real tuner to capture overlapping recordings.


Clear as mud? ;-)
Author:  Too Many Secrets [ Sun Jan 10, 2010 8:10 pm ]
Post subject: 
tjc wrote:
It's funny how the same question will pop up several times in quick succession around here. I was just answering something very like this for kmkittre in this thread - http://knoppmyth.net/phpBB2/viewtopic.php?t=20756

Basically it works like this:

    - A single ATSC or QAM frequency is actually a multiplexed channel (translation - it has several signals combined together).

    - In the ATSC (OTA) world these are typically the sub-channels for a particular broadcaster, e.g here in eastern MA "WGBX44" @ 44.1, "WGBH World" @ 44.2, "WGBH Create" @ 44.3, and "WGBH Kids" @ 44.4 for the local PBS station's second frequency.

    - In the QAM (cable) world there may be as many as 10-12 sub-channels for a given frequency. Even more for the audio only channels with lower bandwidth requirements.

    - When your tuner is set to a particular frequency it's actually receiving all the streams and de-multiplexing (splitting) out just the one(s) you want.

    - Rather than discarding the extra streams, given the right software it's possible to treat them as extra virtual tuners.

    - Once you have that abstraction in place, It's even possible to clone the same stream and treat it as two separate streams. Thus using one real tuner to capture overlapping recordings.

Clear as mud? ;-)


Yeah, what tjc said.
Author:  bkamen [ Sun Jan 10, 2010 8:21 pm ]
Post subject: 
Yea, I think I posted already that I figured it out.

I knew about the mux'd channels and how the transport works -- but wasn't sure how it was handled in MythTV.

Now that I played with it -- it's pretty cool. Myth's interaction was more what I was chasing down.

Thanks for the replies that validated my thoughts.

-Ben
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