[opendtv] Re: virtual channels ???????????
- From: "Donald Koeleman" <donald.koeleman@xxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Sun, 20 Feb 2005 15:44:48 +0100
Virtual channels have been around longer than that in cable and satellite.
Virtual channels were originally just that. Programmes were allocated a
certain value, regardless of their fysical frequency and placement within a
multiplex. I seem to remember that some vendors could offer a virtual
channel option that would indeed hide the actual channel data from the user,
updating the fysical to virtual channel map.
Today you see the same with epg's, the operator assigning slots. Befor
virtual channels, you just had favourites or presets, (radio's, tv sets and
analog satellite receivers and non-operator bound digital receivers).
Basically, to my knowledge(!) directed channel change (as a concept) is what
for instance Microsoft showed at IBC when it refers to the windows media
fast channel changing functionality. Keep taps not just on the channel being
whatched, but on the next and previous in line as well (or others you expect
the viewer will go to next). If you are already decoding said streams you
don't need to wait for acquisition, locking, and thefirst I frame to show
up, befor being able to present the programme to the viewer.
Donald
----- Original Message -----
From: "Craig Birkmaier" <craig@xxxxxxxxx>
To: <opendtv@xxxxxxxxxxxxx>
Sent: Sunday, February 20, 2005 1:59 PM
Subject: [opendtv] Re: virtual channels ???????????
At 11:53 AM +0530 2/20/05, Prashant Desai wrote:
>What exctly is DCC [ directed channel change ) ? i believe its
>required for Ad insertion and using virtual / Physical channels it
>does so
>but i do not know about the concept of virtual and physical channels
>......any pointer using which i can understand the concept of
>
>whats virtual and physical channels ? and whats the purpose of
>having virtual channels
>
This is mostly irrelevant to your project. It is a "virtual" control
layer for ATSC designed to provide continuity for existing analog
channel numbering in the U.S. In essence, if your NTSC channel is 10
and your ATSC channel is 30, you can make it look like channel 10 to
the person operating the receiver.
Directed channel change could be useful in an IPTV system but it
would not require the use of the ATSC methodology, which is part of
PSIP. In essence, the receiver can be instructed to switch to another
channel via a command in the metadata carried in another channel.
This is just an IP routing issue for an IPTV system.
Regards
Craig
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