[mythtv-users] dvd playback with subtitles is jerky

Brian Wood beww at beww.org
Sun Dec 10 00:05:18 UTC 2006

On Dec 9, 2006, at 4:19 PM, Jason Lewis wrote:

> Hi Guys,
> When I play a DVD with subtitles, playback seems to be effected by the
> subtitle rendering. There often seems to be pauses and jerkiness  
> around
> when a new set of subtitles are displayed, as though mythtv is having
> problems rendering them quickly enough.
> I have an  AMD Sempron(tm) Processor 2600+ CPU and I'm using the  
> nvidia
> binary video drivers.
> What could be causing it and is there anything I can do to solve this
> problem short of buying a faster CPU?

I never thought I'd see the day when I referred to a CPU clocking in  
the 2Ghz. range as "slow", but it is in this day and age.

You want to determine if the CPU is actually the bottleneck, and not  
the video system or something else. Assuming you are using an AGP  
video card make sure it's set up correctly. Make sure you are  
actually using the nVidia drivers, just having them installed doesn't  
guarantee they are in use.

You didn't mention what distro you're using, or how much RAM. If you  
are swapping out, adding more RAM would help. Otherwise shutting down  
anything you don't absolutely need to have running might help.  
Running the lightest weight window manager you can would also take  
some load off the CPU. A lot of distros start all sorts of daemons  
that you don't need (sendmail, cups, hal and many others). Use top to  
see what's running. Remember that the CPU usage is just an average  
and even if it shows plenty if idle time you may well still be in  

For example, if you are running a full KDE installation that will be  
taking up a lot of cycles. Looking into something simpler might help.  
Reducing the video resolution might help, depending on where your  
bottleneck is.

If you are doing software multichannel audio that is taking up cycles  
as well.

Cat proc/cpuinfo to make sure your CPU is actually running at the  
speed it should be, some motherboards incorrectly identify what the  
clocks and multipliers ought to be.

Basically the problem is to locate the bottleneck and either widen it  
or reduce the amount of stuff trying to get through it :-)

Just a few thoughts. That machine *should* be able to play a DVD but  
it is marginal under some conditions. A Sempron 3400+ is only around  
$50US so think about a faster CPU (though if you are not in the US it  
will be more $$$ of course).

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