[mythtv] Re: [mythtv-commits] Re: Ticket #126: DVB: avoid unnecessary tuning when already tuned to the target transponder

[Marcus Metzler]

>>>>> "Pekka" == Pekka Jääskeläinen <pekka.jaaskelainen at gmail.com> writes:

    >> No the delay is longer, I'm just saying that these are the
    >> timings from the tune part of the code. (Move this back to
    >> -dev)

    Pekka> OK, so the delay is probably the same for you.

    Pekka> Are you familiar with the DVB code? I started to wonder
    Pekka> that if it's the prebuffering that causes the annoying
    Pekka> delay, could one prebuffer in background all the time
    Pekka> different transponders (as many as possible) so that when
    Pekka> channel is changed, the buffer is already filled? I could
    Pekka> implement this if somebody who knows the code could say
    Pekka> whether it's possible without rewriting most of the code
    Pekka> base.

Tuning times vary widely with the cards. There are cards that can tune
in .3 secs and others that need 2 secs or even more time (I am talking
about DVB-S). In addition to the tuning time you have the time you
need until you can start decoding the MPEG stream, which depends on
the position of the first I-frame and of course on how your program
handles setting the demuxer and extracting the stream from the driver.

The main problem is to write tuning software that works with all types
of cards and is still as fast as possible. of course you can always
tune the delays to your own situation and get much better switching times.

You could also use some tricks to reduce tuning times, e.g.

1) Only tune if you have to, i.e. when you change transponders.
2) Only switch the parameters that change between transponders,
   i.e. leave polarity and diseqc settings alone when they don't change. 

Marcus

-- 
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| Dr. Marcus O.C. Metzler        |                                   |
| mocm at metzlerbros.de            | http://www.metzlerbros.de/        |
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