[mythtv-users] Why does going to live TV take so long?

Steven Adeff adeffs.mythtv at gmail.com
Fri Mar 10 16:42:30 UTC 2006

On 3/10/06, Marco Nelissen <marcone at xs4all.nl> wrote:
> >>> Let's see.  At a minimum, Myth requires 2 or 3 seconds of buffer in
> >>> order to provide the PVR features while watching LiveTV,
> >>>
> >>
> >> That seems rather excessive. There's really no reason to buffer that
> >> much data before starting to play it.
> >
> >Says the guy who didn't write/debug the LiveTV code...  ;)
> Oh, I'm sure there's some problem with the MythTV code that got 'fixed'
> by adding this excessive buffering, but what I meant was that in general
> you don't need to buffer 3 seconds worth of data before you can start
> playing it, PVR features or not. If that was really needed, then all
> digital tuners would have huge buffers and be slow when changing channels,
> and Tivo wouldn't be able to change channels so fast either.
> And for what it's worth: I may be new to MythTV, but I have plenty of
> experience with audio/video software.

Tivo's buffer is about 7 seconds as well. From memory, my Series 1
Tivo had a 7second buffer. The difference is in how MythTV and Tivo
handle the channel change from the perspective of the user. Tivo would
change the channel on the tuner while still playing the current show
until the new channel change had completed and then begin playing the
new show. MythTV orders this differently. When you tell Myth to change
a channel it stops the currently playing channel, changes the tuner
and when it gets a stream begins to play. One could alter this
perception of time by making Myth continue to play the current channel
until the next channel's mpeg file begins filling up with data. The
only issue will arise when the time buffered in the current channel is
not enough to make up for actual tuning time. ie if the tuner takes
6seconds to change channels, lock and begin writing an mpeg file but
you only have 3 seconds of buffer in the current channel then you will
still have 3 seconds of "dead" time.


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