[mythtv-users] Strange problem with jerky playback speed just in live tv - V 0.19

[Matthias Thyroff]

Hello everybody, 

after a recomendation in the forum, I post the description of my problem here; 
I posted in the forum, but there I seem to be the only one who has this 
problem. The original thread is here: 
http://www.mythtvtalk.com/forum/viewtopic.php?p=11869 

Sorry for the long post - I have tried to expose all information I was able to 
collect.  

When I watch live tv on a remote frontend, the playback skips between two 
speeds (it does not stop, it goes slower and faster; as far as it can be 
told, sound is in sync). The periods of slow/fast can be about a second each, 
or shorter, this is not fixed. Eventually, it gets smooth after some time (I 
saw this once, when I left it playing for a couple of hours without 
watching), I do not know what triggers that. When it is jerky, and I open 
iptraf on the server, I can see that the packets also flow "jerkyly" at about 
5000kbit/s; when playback is smooth, the packet flow also looks smooth. Same 
happens with mpeg decoder "default" "xvmc" or "libmpeg2". I have deactivated 
glx in my xorg setup (because of some post if found in google), no change.

The server is about 80% idle when streaming live tv, the harddisk light shows 
activity, but is more time off than on. (is there such thing as iptraf for 
harddisks, so I can see if the bus gets saturated?)

My setup:

Server (backend): Athlon XP 2500 , Kubuntu Dapper, 1GB Ram, harddisk hdc 
(120GB Maxtor; not the fastest disk but should be well fast enough; DMA is 
on) mounted as /tv exclusively for mythtv, reiserfs. DVB-T with hauppauge 
nova-t pci (conexant).

Frontend: Celeron 2GHz, Kubuntu Dapper ltsp (diskless client - server is 
terminal server (no x session active) - mythfrontend as local app), i845 on 
board graphics, connected via VGA to TFT TV (1024x768), 512MB Ram, no 
Harddisk (boots from Server), between 30% and 60% idle during playback.

Network: 100Mbit via 1 switch.

I am not sure if this is related, but sometimes I am seeing a lot of 
messages "rebuffering" on the console.

When I watch recorded programs, it seems to work (it's new, though - not too 
much recorded programs there).

I should try the frontend on the server: I have, but video does either not 
work there due to my beautiful Matrox G550 card :-( or works without xvideo, 
then it is so slow that frames are dropped and I cannot judge. 

Then I tried mythfrontend --verbose playback on the remote frontend with live 
tv and I get messages:

... NVP: Audio is 3.xxxxx frames ahead of video, doubling video frame 
interval.

This could explain variying playback speeds, but this message comes much more 
often (and faster) than than what I could see it going slow and fast: many 
times (>10) per second. 

After a recomendation in the forum, I have checked the option "aggresive audio 
buffer" - it was set. I have removed the option, same problem.

I switched to the console (without --verbose display option), no messages 
there. When I switched back to the video screen, the machine crashed (as 
always - I have to activate framebuffer console, it seems).

Then I restarted the frontend computer, and there, as always in this scenario 
(after a crash, a power shortage (my server is on UPS, the client, not)), I 
cannot watch live tv anymore, because "all inputs are busy recording" (this 
might deserve a seperate thread, looks like a design flaw to me...)

Then I changed to see recordings, and there the actual active live recording. 
I forwarded to the end of the recording to see what should be "semi live tv". 
This is played smoothly!!! Then I restarted the backend - live tv jerky 
Pressed "R", went to the recordings menu to watch live tv (actually, in this 
mode I appearently cannot get closer than like 2 secs to the end), it is 
smooth. 

I then cancelled the recording, went back to live tv - jerky. In live tv, when 
I rewind (to see what has been recorded a few seconds before), jerky! 

Considering that in this version, live tv is treated as a recording (what I 
understood from the wiki), I really cannot see why it does not work for me. 
Actually it seems that the treatment of live tv and recorded tv is not 
exactly the same.

But what's the difference? Can I get my setup working before the world cup 
starts _tomorrow(!)_?

Any help is apreciated; I would love to provide any data that can help to fix 
it. 

Cheers

Matthias