[mythtv-users] Channel Hopping

Dave Sherohman esper at sherohman.org
Tue Oct 4 18:36:10 UTC 2005

On Tue, Oct 04, 2005 at 09:45:45AM -0700, Mark Kundinger wrote:
> There was a recent lengthy (and somewhat heated) thread in the dev list
> about this.  The technical reason for the delay is because the system
> has to do the following things when changing a channel on "Live TV":
> 1) Tune the channel.
> 2) Start encoding the feed.
> 3) Store the file.
> 4) Decode the file.
> Each of these steps takes a little time. If you don't do them, you lost
> the ability to pause or rewind Live TV, which is one of the sexy things
> about a PVR.
> I don't really understand most of what goes on in the developer list,
> but that has been some effort to improve tuning (mainly for DVB cards)
> and store Live TV more efficiently, perhaps doing away with the
> ringbuffer entirely.  So things might get a little better around the
> edges, but there's always going to be some sort of delay (and you'd get
> this delay if you had a satellite, digital cable, or Tivo as well)
> 3)  

My Tivo has been dead for a few months now (which is why I finally
tried myth), but the delay on changing channels with it was
definitely under a second and I remember is as being imperceptible
(although I could probably percieve it if I did a test right now,
but, like I said, it's dead).  I don't know how they manage to do it
so fast, but they do.

I have a separate gripe about the ringbuffer, though:  It gets
unconditionally wiped if the tuner changes channels for any reason.

Now, you may say, "Well, duh...  If you change the channel, then
you're watching something else.", but that ignores the case of the
backend changing channels on its own for a scheduled recording while
the ringbuffer is displaying something from the past.  If this
happens, then you should be able to continue watching from the buffer
up to the point at which the channel was changed.  This is the way my
Tivo worked and I assumed the same would be true of myth - until one
night when I was getting ready to go out and stumbled across Mutant
X.  Not a show that I like enough to watch regularly, but the episode
premise seemed interesting, so I started watching it, then hit pause
and headed to the shower, planning to watch the rest (at an
accelerated rate) while I got dressed.  Unfortunately, I got back to
find that a recording had come up on another channel and I was now
watching that instead of my paused Mutant X and, of course, there was
no way to get back to the now-deleted live buffer, so I never got to
see the end of the episode.

The freedoms that we enjoy presently are the most important victories of the
White Hats over the past several millennia, and it is vitally important that
we don't give them up now, only because we are frightened.
  - Eolake Stobblehouse (http://stobblehouse.com/text/battle.html)

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