[mythtv] ring buffer and live TV

Isaac Richards ijr at case.edu
Sat Apr 15 15:32:04 UTC 2006


On Saturday 15 April 2006 09:11, Daniel Kristjansson wrote:
> On Sat, 2006-04-15 at 14:43 +0200, Felix Rubinstein wrote:
> > Please see my posts on users list by topic "MythTV channel buffer"
> > How is that possible to watch live TV and have PVR: pause, rewind,
> > etc. functionality with S-Video/RCA connection?
> > What was the intention of quite large delay?
>
> MythTV needs to work on many different systems with different
> video bitrates and different levels of hardware performance.
> Hence the buffering requirements are somewhat conservative
> compared to a dedicated piece of hardware. There are many
> things that could be done to speed up channel changing without
> ever touching the buffering code. But if you want this to improve,
> you will have to implement it yourself as LiveTV performance
> is not a huge priority for us. I would suggest benchmarking using
> oprofile as the first step, to find the low hanging fruit.
>
> Then there are other things you could do, for instance the ring
> buffer estimates the number of bytes it needs in the buffer
> based on the bitrate estimate from ffmeg, but this isn't always
> accurate. Maybe if the backend communicated the number of frames
> sent/written it would improve performance, maybe not. At one
> point we found that regular expression parsing of the channel
> entry code was consuming massive amounts of CPU on Mac OS X
> machines, benchmarking might reveal another such surprise.
> There are also many usleeps in the code where a QWaitCondition
> would suffice. Just go at it, benchmark everything and attach
> small independent patches to trac.

I won't accept patches to improve improper use of myth (in this case, not 
changing channels with myth).

Isaac

> -- Daniel
>
>
>
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