[mythtv-users] Prebuffering pause on Frontend playing back BBC HD

Chris Dos chris at chrisdos.com
Mon Jan 1 21:11:06 UTC 2007

Mike Choy wrote:
> I've just built a amd 4200 X2 with 1GIG on asrock motherboard using suse
> 10.2 and packman rpms. The asrock has an on board Nvidia gforce 6100
> GPU, but uses shared memory. On playing BBC HD in the UK (h.264 based
> stream) I'm getting stutter and NVP prebuffering pause on running
> mythfrontend. Have tried all permutations of XV, standard  mpeg decoders
> , deinterlacing etc
> I was under the impression also that playback should not be a problem.

I think that this shouldn't be a problem for mpeg2 playback.  But from what I
understand, the decoders for h.264 in ffmpeg aren't quite up to snuff for speed.
 So your system might not be powerful to playback h.264.  Can you play back
mpeg2 without prebuffering pauses?

> I have recorded the stream and on playback it still stutters. Top shows
> 50.1% CPU utilization.

You might want to hit the "1" key during top to show each individual core's
usage.  It's probably one thread that is maxing out one of the cores.

> As this is a brand new rig  here is what I'm doing to try and trouble
> shoot this. (any further hints and data points also welcome)

Yea, I'm kinda in the same boat as you are.  Are you using SVN?  I don't know if
the packman rpms are MythTV RPMS or not.  I'm running stock 2.6.19 kernel that I
rolled from from kernel.org, Debian Sid, MythTV SVN, and the latest nvidia driver.

> 1. Have downloaded 720p and 1080p h.261 sample movies from  digital
> digest (pirates of the Caribbean)
> http://www.digital-digest.com/movies/pirates_of_the_caribbean2_h264_1080p_trailer.html
>     in Mplayer  top is showing 46%
> 2. Playing the above file under the internal video player is showing 46
> to 49%.
> 3. Playing the recorded stream in Mplayer seems to be a bit better but
> slow frame rate, but It is showing a lot of video corruption.  Also i'm
> getting the error message "too many video packets in the buffer"
> constantly, and Top shows 65% CPU.
> 4. I saw a post where the stutter NVP prebuffer pause was a result of
> poor Aeriel, and I think this might be an issue as I suspect that HD is
> more critical to the quality of the downlink. ( no problems with SD TV
> payback on my system). Will try and use a better downlead as soon as I
> can rig it up.
> 5. Has anyone got a BBC HD recording that is clean that I can download
> to test the system with?

Because you are trying to playback h.264, I don't think there are any hardware
accelerators that you can buy at this point for linux.  I think you're going to
have to do everything in software.  Just like that I'm trying to do.  I can get
away with using XvMC for now, but it's not my ideal solution, and it's not a
solution that will work for you.

I wonder if the developers can start threading the playback app somehow so it
can start using more than one core.  I don't want to even imagine how difficult
that might be to pull off.


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