[mythtv-users] Performance, TV, Network, Video Cards, Identifying bottlenecks (long)

[Eni Gma]

I thought I would go ahead and reply to my own post in order to give a 
progress update.  

Eni Gma wrote:

> -snip-
>
> Frontend Candidate 1:
> AMD k6-2 @ 375 MHz
>
> Frontend Candidate 2:
> Pentium II @ 275 MHz
>
> Frontend Candidate 3:
> Celeron A @ 300 MHz
>
> Frontend/Backend Candidate 4:
> Pentium II @ 333 MHz X 2
>
> Misc Frontend Parts:
> Remote: Creative CIMR 100 IR reciever x 3
> Video: S3 Savage 2000 64MB Composite out x 2
> Video: ATI Radeon 7500 Svid + Composite
> Video: ATI Rage 128 SVid + Comp out, Comp in
> Video: ATI Rage II+DVD Svid + Composite
> Tuner: AI Tech WaveWatcher NeTV-PCI (Zoran zr36120 + Phillips 7110A)
> Capture: Generic BT848 Capture with SVid+Composite in
> Audio: ymfpci, es1370, es1371, oplSAx, opti
> Various Hard Drives, Memory, etc.
>
> Issues:
>
> I am having issues in quite a few areas (and have worked through more 
> problems than I can count to get where I am already) so I will try to 
> categorize the issues:
>
> 1. System Performance: The main issue is performance problems with 
> video playback.  I am unsure whether the issue is with the frontend or 
> backend machines, but I suspect the problem is on the frontend.  The 
> only configuration where I was able to get any acceptable playback was 
> using frontend #2 with the radeon video card.  Also, I am only able to 
> get acceptable playback for live TV, if I am trying to record the show 
> and watch it on the frontend, the playback stalls every .5-1.5 seconds 
> and the audio stutters and cuts out.  The backend is set up to use 
> it's local disk for live TV buffering, but to use the file server via 
> NFS for recordings.  The load on the file server while these 
> operations are happening is negligible.  The processor on the backend 
> machine is usually 50-80% utilization if it is recording and a 
> frontend is playing.  The processor on the frontend machines ranges by 
> machine, but none of them seem to use full utilization during 
> playback.  However, on machines 1 and 3 the playback freezes every 
> second or so, with corresponding audio dropout.  Frontend system 4 has 
> not yet been tested with myth.  Frontend #1 was used as a freevo 
> system in the past, with acceptable performance playing back MPEG2 
> files exported from a TiVo.  One of the drives has MythVideo on it, 
> but it has not yet been tested with the TiVo files.  I am using the 
> default settings for recording live TV and scheduled recordings. 
> So I guess my question in this area is what are the minimum system 
> requirements for a frontend system?  Are any of the candidates listed 
> above going to be able to cut it in the performance arena?  Do I just 
> need to optimize the way things are set up on the systems that can't 
> play video well (or the backend system) or are they simply too 
> underpowered and no amount of optimization will suffice?

I have been able to get frontend system #1 to play live TV adequately by 
clocking it to 100x4.5.  It really pepped it up to up the bus speed, it 
was running at 66 MHZ before.  It is using the Rage II card (see below) 
running Myth/Blackbox/X in a custom runlevel.  The CIMR-100 remote 
reciever is working well, although I wish the remote had a few more 
buttons.  Also, mythfrontend will segfault if you send it certain 
keystrokes (like KP_Space).  I am almost ready to roll this system out 
to the roomates for testing.  I am also setting up candidate 4 as a 
backend server.  It has the bt848 capture card, as well as the 
WaveWatcher tuner card (sure, it doesn't work, but maybe it will at some 
point in the future).  Myth is compiling as I type, hopefully soon I 
will see how Myth integrates multiple video sources.  This will also 
hopefully give me another point of reference in my attempt to identify 
where my recording setup is going wrong (see below).

>
> 2.  Network Performance.  As I stated above, I am attempting to use a 
> remote NFS server for storing recordings.  When I am trying to record 
> something and watch it on frontend 2 (which can watch live TV with 
> almost acceptable performance) the video stutters as described above.  
> I am wondering if these problems are related to network performace.  
> The NFS server and the backend server are connected via a 24 port 
> netgear 100 Mb rackmount hub.  During the testing phase the frontends 
> have been connected to a 8 port 100 Mb D-link switch.  Is it possible 
> that my problems viewing programs that are recording are related to 
> network performance?  What are the bandwidth requirements for 
> recording (and playing back) programs?  Are there other people who are 
> using NFS mounts to record programs?  With so many variables (backend 
> performance, frontend performance, network performance, file server 
> performance, etc.) it is hard to narrow down where the problems are.  
> Is it possible that I need to upgrade to a switched network for the 
> backend servers (or even gigabit??).  Or are my problems related to 
> system performance and not network performance?

I have switched the hub connecting the backends with a switch, so now 
they are connected full-duplex.  I am still seeing the same problems 
with network playback.  I think it is less a network problem than a 
codec problem.  As I was browsing the settings, I noticed that the live 
TV was using MPEG4, while the default was using RTJPEG.  I think this 
may be the difference when I am watching recordings rather than the 
network.  I will need to conduct further tests in this area to 
positively identify the problem.  I was under the impression that MPEG4 
required more processor, but it seems that my low-powered front-end 
systems play it better than the RTJPEG.  It does not seem like it takes 
a great amount of bandwidth (perhaps a maximum of 1 MB/second when 
recording and 2 frontends playing) and the backend, frontend and file 
server boxes all seem to have plenty of idle time.  I really don't know 
where the bottleneck is.

>
> 3.  Video Out.  As you can see from the array of video cards listed 
> above, I have tried quite a few things trying to get the video signal 
> to my television.  I need either s-vid or composite output that works 
> in X, but so far, none of the listed video cards can give me that.  
> Has anyone used any of the cards listed above for output to a 
> television?  When I was using system #1 for freevo, I used one of the 
> savage 2000 cards listed above.  I was enthusiastic about this card, 
> because it gave acceptable video playback under freevo and the 
> composite output worked automatically under X, as opposed to all the 
> ATI cards listed above, which seem to have problems displaying X on 
> the alternate outputs.  So enthusiastic in fact, that I bought another 
> one for use in my envisioned video network.  Unfortunately, once I 
> tried to use this card with MythTV I discovered that it did not 
> support XV accelerated output and on further investigation, I don't 
> know if they ever will have XV support.  Does anyone else have this 
> card, and are there any workarounds for using MythTV with cards that 
> don't have XV support?  The card really does a good job of outputting 
> X to the TV, and I would love to be able to use the two cards that I 
> have in some capacity.  The ATI cards all have tv-out support under 
> windows, but so far I have been unable to get them to work at all 
> under Linux.  Are there alternate drivers available that might help me 
> out on the ATI front?  I have looked at the Gatos drivers, but the 
> documentation is unclear on what cards are supported and what features 
> are supported with each card.  Is there anyone that is using one of 
> the above ATI cards that successfully uses the TV-out under Linux?  Or 
> does everyone use scan converters?  All the scan converters I have 
> seen are quite expensive and I am reluctant to purchase one (or many) 
> when I have all these video cards that have the hardware to output a 
> composite signal.  None of the frontends are going to be used for 
> fancy displays, they just need to be able to output a decent composite 
> or s-video signal to a normal television.  I would certainly prefer to 
> use the many cards I have listed, but if I am unable to, can someone 
> recommend a card that will work flawlessly for tv-out under Linux?  I 
> would like to spend as little money as possible, as I have already 
> sunk a ton of money into this and I am likely to end up with a bunch 
> of hardware that I cannot use.  I have seen many posts about the 
> NVidia cards, will something like the 440 mx (or similar) give me the 
> TV output that I need?


WOOOHOOO I got TV-out working on one of the cards listed above. 
 Unfortunately, it was one of the lower-powered cards, the ATI Rage 
II+DVD.  But it at least has XV support, which the Savage 2000 cards are 
lacking.  Myth just segfaults if I try to use one of the Savage cards. 
 For info and patches for TV-Out on Mach-64 based cards, see 
http://www.retinalburn.net/linux/tvout.html.  I welcome any info on the 
Rage 128, Radeon 7500 and the other cards listed above.  I would like to 
have at least 3 frontends, 1 working video card is probably not going to 
cut it ;-\

>
> 4.  Audio.  When I am watching video on the system that nominally 
> works (frontend 2) the audio is out of sync.  When I start watching 
> the video, the terminal gives an error to the effect of "Can't query 
> audio buffers on this card, audio will be out of sync".  I believe the 
> card was the Yamaha using the ymfpci module.  Is there something I can 
> do to fix this, or am I just out of luck with this sound card?  Would 
> it suffice for the backend machine (which is currently using an es1371 
> card)? 
> Also, I was wondering about the btaudio module.  Has anyone used the 
> WinTV-go with btaudio successfully?  I have loaded the module, and it 
> sets up /dev/dsp2 and 3 (digital and analog), but piping the output 
> from those dsps to the sound card only gives popping or nothing.  
> Currently, I am using the analog output into the sound card line in, 
> but I would love to dump the sound card on the backend to make room 
> for additional tuners.   


No progress on the btaudio front, looks like I am destined for a sound 
card, at least for the near future.  I have switched to an es1370 card 
for frontend 1, it seems to keep Live TV in sync fairly well.  Recorded 
material is another matter...

>
> I also have an alternate video feed that has a single channel that I 
> would like to distribute with Myth.  I was thinking of purchasing an 
> old secondhand VCR (or cable box) and piping the channel onto the 
> composite input of the generic bt848 card that I have.  How should 
> this be set up?  I obviously need to set this up as a second video 
> input, but how do I set up the listings side of it.  I pull the XMLTV 
> listings manually for another application, and have been using 
> mythfilldatabase --file to load the file (which also contains the 
> channel on the second cable feed).  Do I need to do a second xmltv 
> pull that gets just this channel and create a input entry for it?  How 
> will it appear in the EPG?  Will it be on the very end since it is a 
> different input source or will the channel number sort itself in with 
> the existing channels?
>
> Concerning the AI Tech WaveWatcher NeTV-PCI (Zoran zr36120 + Phillips 
> 7110A), has anyone used this thing?  There are drivers in the kernel 
> source, but they are seriously broken and set up to use the old i2c 
> interface.  Does anyone know if there has been any effort to port the 
> drivers to the new i2c interface?  Or are these drivers going to fall 
> by the wayside and I will have another useless piece of hardware.

Would love for this card to be my second tuner, does anyone on this list 
have enough i2c knowledge to port this driver to the new interface?  I 
notice there is a handy HOWTO in the 2.5 kernel sources on how to do it, 
but I'm afraid the skills required are still beyond my abilities (I 
tried, with less than stellar results).  As before, any tips or comments 
are appreciated.

>
> TIA for any advice.
>