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

Mark Knecht markknecht at gmail.com
Fri May 2 16:16:39 UTC 2008

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

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.


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