Jittery Video?

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mdaria510 Offline
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Post: #1
I was hoping the new beta 2 would fix the problem, but its still evident.

The issue being that the video does not play at an even rate, there is a very slight jitter in the video. It would mostly noticeable during pans for most people. However, the TV I have my HTPC hooked up to is one of those newfangled 120hz sets that can interpolate the image to look super smooth. It only works properly for movies when the output is a clean 24fps - a single dropped or delayed frame here or there screws it up.

When playing the same videos in Vista Media Center, Mediaportal or Media Player (DVDs, .mkvs, .wmvs, etc), they play back in sync, and the 120hz interpolation will lock in. Any video in XBMC is a no go for that. I've tried just about every setting imaginable that might have an effect on it and it seems like its just an internal issue.

To be clear, these arent frames being dropped. Pressing O to bring up the stats will not show dropped frames, and the CPU usage is no higher than 40%, even on HD videos. The a/v quickly fluctuates between 0.000 and 0.040 or so.

Setup:

Intel Pentium Dual Core 2.0ghz
Nvidia 8400 GS
2gb RAM
Vista Home Basic

Any ideas?
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ashlar Offline
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Post: #2
This is exactly what I was hoping *not* to read.
I have super smooth pans with Reclock+VRM7+Zoom Player at 48Hz. I don't want to take a step back... but I so want to use XBMC Sad
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harlekin Offline
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Post: #3
There already has been a similar thread on this, but maybe now is the time to tackle the problem. The effect is most apparent as said before on horizontal pans, but also visible during vertical ones and scrolling credits.

If this should turn out to be a video card problem, I'm on ATI.
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Jezz_X Offline
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Post: #4
ashlar Wrote:This is exactly what I was hoping *not* to read.
I have super smooth pans with Reclock+VRM7+Zoom Player at 48Hz. I don't want to take a step back... but I so want to use XBMC Sad

Well you know you can always just try it and see ?
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Berz Offline
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Post: #5
I've installed XBMC on two very diferent PC's, both brand new Dual Core Intel and AMD specs (around 3Ghz). I have been tweaking and trying different things since Alpha 3 but it's identical on both PC's. When I watch horisontal pans in 720p (my TV doesn't support 1080p) it jitters just slightly like "mdaria510" mention. The infamous Planet Earth: Bird scene plays fine without any stutter. There might be things I haven't tried, but it's not that big a deal. I have the feeling it's something that will go away as XBMC matures over the next months and the internal codecs like ffdshow gets some more revisions..
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WiSo Offline
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Post: #6
Did you first notice the jitter with beta2 or also earlier?

Always read the XBMC online-manual, FAQ and search the forum before posting.
Do not e-mail XBMC-Team members directly asking for support. Read/follow the forum rules.
For troubleshooting and bug reporting please make sure you read this first.
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eyelander Offline
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Post: #7
Same problem for me. Small stuttering when camera is panning on my 42" LCD.

XBMC have always given me this problem. (plays fine with MPC, MP and more).

E6400 3GHz dualcore
GForce 8600GT
2Gb Ram
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ashlar Offline
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Post: #8
Jezz_X Wrote:Well you know you can always just try it and see ?
I tested one of the alphas and plan on testing this new beta for sure.
It's just that if you go here: http://forum.slysoft.com/showthread.php?t=19931 you can see that this is *not* a simple problem.
Obtaining smooth pans throughout a movie's length it's not an easy task. Too many different clocks working on a PC for that. CPU clock, video card clock, audio clock... they all have to be synchronized somehow.
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ashlar Offline
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Post: #9
eyelander Wrote:Same problem for me. Small stuttering when camera is panning on my 42" LCD.
Just to be sure: you are on an exact multiple of the frame rate as far as refresh rate is concerned, right?
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mdaria510 Offline
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Post: #10
ashlar Wrote:Just to be sure: you are on an exact multiple of the frame rate as far as refresh rate is concerned, right?

well, from what I can tell that seems to be the root of the problem. Xbmc is htpc software, and therefore it's primary use will be on a tv. Virtually all tvs are locked at a 60hz refresh.

The proper way to play back a 24hz film on a 60hz set is to use the 3:2 cadence. From what I can tell, xbmc doesntb even try this and just spitz a frame out when it's ready at the next screen refresh.

Now I might have a 120hz tv, but that doesn't mean I can set the refreshrate to 120...60hz is still the max. If xbmc were to do the proper 3:2 cadence, the tv would pick up on it and smooth it out.

Until xbmc can do the most basic thing (play films properly on a tv), I can't see how it can be used as htpc software. It's a hair away from greatness right now.
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mdaria510 Offline
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Post: #11
And I've noticed this on alphas through the latest beta. I was hoping the new multicore decoding would fix it, but it's an issue on even the lowest bitrate mpegs.

I would suspect that it might work fine on a 48hz refresh if the refresh rate is the root of the problem. But that's simply not an option on a tv.

Whatever the issue is, however difficult it is to do, it MUST be done. Right now, xbmc is like a ferrari that can't get you from point a to point b. I don't wanna drive the old civic any more. Sad
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tslayer Offline
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Post: #12
Gotcha, but without a way for devs to reproduce, it is hard for us to help.

My videos all play perfectly.

42.7% of all statistics are made up on the spot

Always read the XBMC online-manual, FAQ and search the forum before posting.
Do not e-mail XBMC-Team members directly asking for support. Read/follow the forum rules.
For troubleshooting and bug reporting please make sure you read this first.
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mdaria510 Offline
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Post: #13
Understandable, as it might not be plainly obvious in most cases. But on my tv, it's night and day because I can plainly see whether or not the 3:2 cadence is there for the interpolation to lock on. There might be little I can do coding-wise to help, but my setup can be a perfectly objective test for any fixes/changes regarding the issue.

I'm curious...is this an officially recognized issue by the xbmc devs, or is it really a matter of "we can't reproduce it, so there's no issue"?
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midgetspy Offline
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Post: #14
My XBMC has always done this as long as I've had my HTPC. It's extremely difficult to notice except on specific panning scenes, though, and I bet the vast majority of people have never noticed (and when people say "my XBMC works fine" they just can't tell). It's done this on 3 totally different hardware setups and 2 OSes.

The only place I usually notice it is in nature shows like Planet Earth. Recently I noticed it in a single scene in Cars. If you pay attention to a single edge during a pan you will notice that it is not moving smoothly but is slightly jerky. It never stops moving, but it just slows down and speeds up slightly as it pans. I always assumed it was just another XBMC <-> ffmpeg issue, but maybe if it has to do with fps/Hz it'll be simpler than that to fix?
(This post was last modified: 2008-10-07 18:24 by midgetspy.)
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mdaria510 Offline
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Post: #15
yeah, that's my guess as well...that it's so subtle for most people that they might not b aware there's an issue.
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