[mythtv-users] Stuttery playing back BBC HD

Paul Fowler Paul.Fowler at reuters.com
Tue Jan 2 12:42:39 UTC 2007


I have been experimenting with BBC-HD and have got to the point where I
need to re-check some of my assumptions because although I get
beautifult crisp pictures, I am not getting full frame rate. Furthermore
it is not like I am getting every other frame dropped, I seems to run
happy for about 8 frames at a time then pauses for about a half second.

My hardware is (in my experimental system):

CPU: Athlon 2400+
Motherboard: Abit NF2-s Nforce 2
RAM: 768MB DDR mixture of PC2700 (256MB) and PC3200 (512MB)
Hard Disk: 80GB (hdparm -t /dev/had reports 45MB/s) on 80wire cable
using dma
Tuner card: Twinham VP1020A satellite pci card (latency_timer = 32)
Video card: Nvidia FX5200 64MB AGP (latency_timer = 248 - not sure if
relevant)
OS: Fedora Core 4 latest kernel 2142

I admit this is a bit of a hotch potch of parts, but I wanted to proove
this out first.
Using MythTV 0.20 I get the same stuttering whether using standard,
libmpeg2 or nvidia_xvmc
I have the nvidia driver installed from atrpms (7676 I think??)

My present concerns are:
1) can the twinhan card handle the symbol rate which BBC-HD uses (not
sure how to test this)
   so far I have tried playing the recorded files (eg Planet Earth
8.6GB/Hour!) on various machines including a P4HT 2.8GHz and still
cannot get the full frame rate - eg. I am not sure if the disk files are
correct.

2) I believe my hard disk is fast enough (although ridiculously small)
on this test machine, but not sure if ext3 filing system is killing
performance ?

3) probably the CPU is not fast enough.

4) I know XVMC is working, but not sure if it is helping me with H264
transport streams ?

I have tried fiddling with latency timers, I believe my hard drive speed
is up to it. I have done chmod a+s on /usr/bin/mythfrontend. I have
added group mythtv to /etc/security/limits.conf to try and establish
realtime priority (but think I need @mythtv rather than @audio, but as I
do not know much about users/groups I have probably done that wrong).

I plan to try szap "BBC-HD" and dvbstream | mplayer soon to see what is
possible, and to try mplayer with -benchmark.

Can anybody suggest an in-expensive adjustments I could make, or other
things I could check.

Regards,
Paul.


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