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PostPosted: Thu May 07, 2009 2:09 am 
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I'm having significant problems getting decent video playback out of my system. I've been fiddling with various settings for about 6-8 hours or so now, and I can either achieve settings that play back Live TV okay, or play black recordings, but not both. I'm at my wits end and am just not sure what's going on anymore.

The machine in question is a slave FE/BE connected over Ethernet to a master FE/BE elsewhere in the house. It's a P4 2.4GHz, and I've used it in the past to playback SD just fine. (In fact it used to be the master FE/BE.) It has a NVidia GeForce 5200 and it's connected to an SD TV via S-Video out of the 5200.

It wouldn't play back HD though, and was having "hiccups" when playing SD (seems like this has just developed since the last time I reinstalled everything, or maybe the upgrade to the latest version, I'm not sure), so I tried to find a better set of playback settings.

What I've found is basically this:

If I use the "CPU--" setting and watch live SD off the internal PVR150 tuner, the output looks great. The log tells me that it tries to use ivtv, but because I don't have a PVR350, it falls back thusly:
> 2009-05-07 02:57:35.817 VideoOutputXv: Desired video renderer 'ivtv' not available.
> codec 'MPEG2' makes 'opengl,xv-blit,xshm,xlib,' available, using 'opengl' instead.
Basically, it seems to fall back to opengl and use that when ivtv doesn't work. Fine, makes sense.

But if I take that same "CPU--" setting and try to watch a recorded/transcoded video, I get a black screen. The log doesn't really show anything interesting, except "codec 'NUV MPEG4' makes 'opengl,xv-blit,xshm,xlib,' available, using 'opengl' instead." So it's trying the same fallback, but for whatever reason it's just showing black. Once it goes black, I have to manually kill mythfrontend or restart XWindows to recover.

If I create a new playback settings profile and try to manually select the opengl renderer, it doesn't work for live TV at all. This doesn't make sense to me -- it works as a fallback from ivtv, but not when I select it manually?

If I use the 'Slim' profile, Live TV plays back but "hiccups" every few seconds. Basically the video freezes in place, the audio continues, and after a second or so the video will abruptly catch up. Sometimes I get "NVP: prebuffering pause" messages in the log, sometimes I don't. During these 'hiccups,' the processor utilization on mythfrontend spikes to 99%, despite normally hovering around 40% or less when playing SD. This basically results in unwatchable video. Recorded content, though, plays back fine with 'Slim.'

This just doesn't make sense to me; I've got one setting that works fine for live TV but not recordings, and another that works fine for recordings but produces crappy performance on live, and one of them seems to use a setting (opengl) that doesn't work at all when I set it manually.

Can anyone help? Eventually I'd like to be able to watch SD and HD on this machine, but right now I'd settle for just being able to watch both live and recorded SD without any hiccups or black screens.


Last edited by Kadin2048 on Wed May 20, 2009 4:36 pm, edited 1 time in total.


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PostPosted: Thu May 07, 2009 5:47 pm 
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Joined: Thu Mar 25, 2004 11:00 am
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Location: Arlington, MA
The first debugging question is always "what's different". Here the difference between your "live" and "recorded" seems to be the encoding. Given the MPEG4 error I'd guess that you're using a YUV capture card (framegrabber/software encoder) and transcoding from RTJPEG to MPEG4 (although you could also be using a PVR card and transcoding from MPEG2 but that's very rare). In either case, it looks like the playback profile you're using doesn't include support for MPEG4 video. Unfortunately, unless you have an Nvidia card that supports VDPAU and the newest generation of their drivers to take andvantage of it, there isn't any accelerated support for MPEG4 playback.

I'd suggest a visit to the MythTV wiki (not the KnoppMyth one) page on playback profiles and see if it mentions MPEG4. You may also want to search their mailing list.

http://www.mythtv.org/wiki/Playback_profiles


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PostPosted: Thu May 07, 2009 7:01 pm 
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tjc wrote:
Given the MPEG4 error I'd guess that you're using a YUV capture card (framegrabber/software encoder) and transcoding from RTJPEG to MPEG4 (although you could also be using a PVR card and transcoding from MPEG2 but that's very rare).


Thanks for the response, tjc.

I'm actually using a hardware MPEG-2 encoder card, not a YUV framegrabber. (It's a Hauppauge PVR-150.) I have most recordings set to transcode to MPEG-4 after recording, to save space on the backend; that's where the MPEG-4 is coming from.

So live TV is coming in off of the PVR150 and is MPEG-2, and most recordings are transcoded and are MPEG-4.

Does that shed any light on the issue? Any suggestions as to what profile I ought to be using, given my playback hardware? (P4 Prescott 2.4GHz, NVidia 5200)


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PostPosted: Fri May 08, 2009 8:40 pm 
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No idea what profile you need, but it pretty much explains the problems you're having.

I don't know how much difference going from MPEG2 to MPEG4 makes but big HDs are *cheap* these days, and most of us don't bother. Just clipping the commercials with the lossless MPEG2 transcoder gets me 20-40%. Which means that the BE claims to have 9 days 21 hrs 15 mins of recorded material using under 385Gb out of 445Gb. That's a LOT of recordings.


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PostPosted: Wed May 20, 2009 4:34 pm 
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Well, I spent a while playing with things and eventually found that if I dropped the screen resolution from 1024x768 -- which was what it defaulted to -- down to 800x600, suddenly the video worked just fine with ffmpeg and the other software components.

So that's what I did ... unfortunately this caused a totally different problem with the menus becoming very slow, which I'll open a new topic for.

The bottom line was that apparently playing back 1024x768 was just too much, but 800x600 is smooth as silk both from LiveTV (MPEG-2) and transcoded recordings (MPEG-4).


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PostPosted: Wed May 20, 2009 8:56 pm 
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Joined: Thu Mar 25, 2004 11:00 am
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Location: Arlington, MA
Must be the lack of acceleration with MPEG4. XvMC really makes a huge difference, but it only works with MPEG2 content. Right now I'm watching live HD at 1080i (1920x1080@60Hz) on my FX5200 and top shows between 54% and 61% idle.

Outputting to a NTSC SDTV you'll almost always get the best results using a 640x480 output resolution. Better picture quality, lower CPU load, ... This is one of those cases where more is *NOT* better. Match the output resolution to the screen resolution and any number of odd problems go away. Does your picture look washed out? Are there scaling artifacts on diagonal lines and curves? Is Bob2X deinterlacing not usable because you don't have enough bandwidth on the dot clock?

FYC here's the current hardware spec
Quote:
Antec SLK1650B
Epox EP-9NDA3+ Nforce3 939, Athlon 64 3200+ "Venice", Zalman 7000B-AlCu
Kingston KVR400X64C3AK2/512, Kingston KVR400X64C3AK2/1024
128MB AGP FX5200
PVR-250 Model 980, PVR-150 Model 1045, pcHDTV HD5500
NEC FD1231H-302 FDD, NEC ND-3520A DVD
2 Seagate ST3250823A
Samsung LN46A650


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PostPosted: Thu May 21, 2009 9:14 am 
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I might give dropping it to 640x480 a try, then, just to see if there's even more improvement. I'm a bit flummoxed by the slow-menus issue that came up though, and I think I need to get that worked through before I can play with the resolution some more.


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PostPosted: Thu May 21, 2009 9:51 pm 
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Joined: Thu Mar 25, 2004 11:00 am
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Location: Arlington, MA
Slow menus usually mean something else is wrong, but being a bit fried the old brain isn't remembering exactly what right now. :( It's a classic issue though, so a good search should turn it up.


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