[mythtv-users] LiveTV: stutter at program start/change resolved by short pause..?

[Nicholas Fasano]

> >> I'm seeing this too, especially with high bandwidth channels, for 
> >> example HD content. Defragmenting the XFS storage improved the 
> >> situation a bit, but not completely, and it gets worse again after a 
> >> while. 
> >> I don't see this behaviour always, but regularly. Another symptom of 
> >> what I guess has the same cause, is some loss of stream content 
> >> during the program change. The video/audio almost freezes for 1-2 
> >> seconds, dropping a frame or two during this pausing, and then 
> >> either continues normally, or with the symptoms you describe. 
> >> Programs that are being recorded in the background during that 
> >> freeze/frame loss usually lose a few frames too. 
> > 
> > same problem here too. And it occurs on nearly each program change. The 
> > backend has a problem to switch fast enough to the next file, therefore 
> > the frontend gets stuck. Sometimes it lasts too long and the frontend 
> > jumps to main menu with a video-buffering error. 
> > On H264 content often the first frames are broken (perhaps new file 
> > don't start at a keyframe?). 
> 
> If you don't mind, I'm going to hijack my own thread back! ;-) there's already low enough traffic and interest on this that I'd hate having it go in another direction... 
> The problem that I and others are referring to is not caused by channel changes: You start listening to a livetv program. It's choppy. pause-unpause and it's fine. Then your show ends and a new one begins, same channel. Choppyness starts again. pause-unpause. your good again. 
> 
> Thanks! 
> Daniel

I'm going to attempt to re-hijack this thread.  I can confirm that the "always stream recordings from backend" setting has no effect on the behavior that Daniel and I are reporting.  Can anyone else shed some light on this?  Does anyone else experience the issue?  I will repost my initial description for convenience:

> Hello everyone, 
> 
> I just finished setting up my new mythbox (replaced my old mythbox that's been chugging along for over 5 years now) and I now have everything up and running perfectly. Except for one odd glitch. It's a prebuffering pause that doesn't seem to be listed on <http://www.mythtv.org/wiki/Troubleshooting:Prebuffering_pause>. Occasionally, only when tuning LiveTV on an HD channel, I will get repeated prebuffering pauses corresponding to brief skips in audio and video. Toggling the pause button for an instant completely fixes the problem until a new channel is tuned. This doesn't happen every time I tune an HD channel, and I haven't been able to figure out what actually causes it. It only occurs on HD channels from my HDHomerun. It hasn't happened yet with the HD-PVR, but I just got that up and running over the weekend and haven't used it that much yet. 
> 
> Here's my setup: 
> Foxconn P55MX Motherboard 
> Intel i5 Quad 2.66 GHz processor 
> 4GB RAM 
> MSI N220GT-MD512 GeForce GT 220 512MB Video Card 
> 
> PVR-250 on PCI bus 
> HDHomerun 
> Hauppauge HD-PVR 
> 
> I'm using a clean install of Ubuntu 9.10 with just the standard repositories. The mythtv version that this pulled in is fixes22594. I did try upgrading to the weekly Mythbuntu repositories, but that didn't help. I am using the VDPAU High Quality profile with no VDPAU issues, and I have tried all the different VDPAU profiles and deinterlacers. My hard drives are not dying. It's not a problem with my system's CPU or graphics card's capabilities. They can both handle pretty much anything thrown at them. I can play a full bitrate blu-ray file without a glitch using 2% CPU. I'm not a developer, but if you ask me the problem is that mythtv is trying to play video too close to "live". I think I just need to get mythtv to buffer a few more frames so it doesn't get ahead of itself. I have tried many different settings for the HD Ringbuffer, and that doesn't help. There's no problem with the video files, as this never happens with recordings, just live 
> tv and it always resolves by just briefly pausing the video. It's not really a major issue, but I have a relatively 'plain vanilla' setup so there's got to be many others who have the same issue but are not taking the time to document and post it. I have searched the lists and there is one thread on the dev list which sounds similar, but the details are sketchy. I may be suffering from the "Accepted Defect" described here: <http://svn.mythtv.org/trac/ticket/6922>. With so many users using VDPAU and HD sources, I'm surprised this hasn't attracted much attention. 

This happens on my combined FE/BE system as well as all three of my remote frontends, all using VDPAU.  My system is now using the latest 0.23.1 fixes (26732).  The backend is a GT220 and the frontends are all Zotac ION systems.  Again, the "always stream recordings from backend" setting has no effect on the behavior.

Thanks,
Nick