[mythtv-users] 5min jump takes long during time shift

Douglas Wagner douglasw0 at gmail.com
Tue Jun 2 21:39:29 UTC 2009

On Tue, Jun 2, 2009 at 4:18 PM, Thomas Börkel <thomas at boerkel.de> wrote:

> HI!
> I have the problem, that a 5min jump forward takes sometimes up to 15s
> when watching a show while it is being recorded (for example 30 min
> behind real time).
> 20s jumps are no problem.
> Anyone knows, what that is?
> - seperate backend and frontend (diskless PXE)
> - gigabit ethernet
> - optimized mysql settings
> - backend: Athlon 64 X2 DualCore 3800+, 1 GB, kernel 2.6.25
> - frontend: Celeron 2.6 GHz, 512 MB, kernel 2.6.28
> - both systems running Gentoo
> - Myth 0.21 fixes
> - no NFS for recordings (backend is streaming)
> - no comm flagging during recording, but after recording
> - MPEG2 (DVB-S)
> - SDTV, displaying on full HD
> - no frame-perfect jump configured
> Thanks!
> Thomas
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> mythtv-users at mythtv.org
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I almost hesitate to respond to this because I really have no sure clue
here, but the fact you're running a separated frontend/backend and STREAMING
the data, your frontend system is a Celeron 2.6GHz (VERY slow for HD
processing), and you're jumping forward so far in a broadcast, I would think
all work together to cause the problem.

My suspicion (and I will let the more knowedgeable on the list correct me)
is that when you press that "jump forward 5 mintues" button, the backend
needs to move the video stream forward that amount.  It's likely that there
isn't 5 minutes worth of buffer in place for a video comming across at 1080i
or 720p (that's ALOT of data...even though it's an SD recording, you're
still having to stream it at 1080?  Or is that the front end that's doing
the conversion from 640i/p to 1080i?  I forget).

I have seen during my video editing escapades (grrr) that jumping forward,
even a small amount, causes a couple seconds of delay on a slow
box...between the streaming, the network, the video size, the buffer or lack
of one, the amount of data you're having to skip, and the slow CPU speed of
your front end, I suspect this is all part and parsal of the problem you're

In other words, I don't know that this isn't normal behavior for your setup.

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