[mythtv-users] Recorded material stutters, live TV is perfect. Why?

Mark Boyum circushair at gmail.com
Fri May 2 17:05:18 UTC 2008


On 5/2/08, Mark Knecht <markknecht at gmail.com> wrote:
>
> On Wed, Apr 30, 2008 at 7:18 AM, Mark Knecht <markknecht at gmail.com> wrote:
> > I'm flummoxed about 0.21 and all the stuttering problems we're having.
> >  Here's the set of experiments I've done:
> >
> >  The system:
> >
> >  1) The backend - dedicated backend machine is an AMD Sempron 3200+,
> >  with SATA drive & 512MB. hdparm -tT says 45MB/S. After a boot I'm
> >  using 180MB of ram. No swapping has been reported.
> >
> >  2) Local frontend - underpowered 1.8GHz Celeron with 256MB, but shared
> >  memory with the graphic controller so only about 185MB.
> >
> >  3) Remote frontend #1 across wireless network - AMD64 3000+ with 1GB
> memory.
> >
> >  4) Remote frontend #2 across wireless network - identical to local
> >  frontend - 1.8GHz Sempron with 256MB.
> >
> >  The results:
> >
> >  1) On the local frontend I can run live TV or recorded material
> >  without any stuttering.
> >
> >  2) On remote frontend #1 (the AMD64) I can run live TV without
> >  stuttering but all recorded material stutters badly. The AMD64 is
> >  running the SLIM profile.
> >
> >  3) On remote frontend #2 I have no problems. Live and recorded
> >  material playback fine.
> >
> >  Prior to switching to 0.21 we had no problem with any machine. Since
> >  switching to 0.21 my AMD64 machine is useless.
> >
> >  CPU usage on the backend is never more than 2% when it's only doing
> >  playback. On the AMD64 CPU usage as reported by top is never more than
> >  20%.
> >
> >  Here's the one that really bothers me: On the AMD64 I can play live TV
> >  with a full system rebuild going on - compilers are running and CPU
> >  usage as reported by top is 100%. Disk usage is intense at times. Live
> >  TV is perfect. No stuttering. On the other hand with absolutely
> >  nothing running on the AMD64 playback of recorded material stutters
> >  all the time.
> >
> >  I cannot figure out where the weak link is.
> >
> >  Any ideas anyone?
> >
> >  Thanks,
> >  Mark
> >
>
> OK, so no one has any ideas yet. Hopefully this info will help:
>
> 1) While running the AMD64 frontend in Linux I ran mythfrontend and
> along side it ran top. When I first start playback it is at regular
> speed and top shows 10% CPU usage. At this point I can play recorded
> material without much stuttering. It's almost as good as live TV, but
> not quite.
>
> 2) As is my custom I typically watch recorded TV shows 10% fast. ('a'
> key, right arrow twice) With 0.20 I could do this and there was no
> noticable change in CPU usage. It stayed in the 10-12% range. With
> 0.21 the CPU usage jumps to over 20% and this is when the stuttering
> gets really bad on this machine.
>
> 3) When I drop the speed back to normal ('a' key - left arrow twice)
> the CPU usage stays at 20%. Nothing I do makes it come back to 10%
> like it is when I tart clean. At this point the frontend still
> stutters.
>
> As an additional test I boot the same machine into Windows XP. In XP
> the MythTV player application stutters just like Linux but it does it
> at normal speed. I get messages about rebuffering.
>
> On this same machine in Windows XP the NetFlix Instant Watch player
> plays fine for hours without stuttering or rebuffering.
>
> Unfortunately this machine has an ATI controller in it so I'm not able
> to do XvMC, as far as I know. If there are accelerations I can enable
> I'd like to find some instructions on doing so.
>
> Thanks,
> Mark
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>

You haven't indicated what type of material you are recording / playing.
Assuming it is SD, I would say that even at 20% your system should be able
to perform decent playback.  I would suspect the problem is related to using
a wireless network.  Just to test, try connecting that frontend via Cat5.

I am no expert on Myth, but that is my 2 cents.
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