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

Mark Knecht markknecht at gmail.com
Fri May 2 17:15:24 UTC 2008


On Fri, May 2, 2008 at 10:05 AM, Mark Boyum <circushair at gmail.com> wrote:
>
>
> 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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> > mythtv-users at mythtv.org
> > http://mythtv.org/cgi-bin/mailman/listinfo/mythtv-users
> >
>
>
> 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.

Mark,
   I'll do that but over the weekend as I'll have to physically take
the machine to the other room.

   I don't know how to gauge how much data the NetFlix system is
transferring but it seems to buffer a LOT of data before it starts
playing. 20-30 seconds. Once it starts playback it's flawless. Myth
doesn't buffer anything near that, I suppose due to commercial
skipping and the like.

   Yes, it's all SD recorded from either a PVR-150 or a 250.

Thanks,
Mark


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