Jittery Video?

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.

Gotcha, but without a way for devs to reproduce, it is hard for us to help.

My videos all play perfectly.

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"?

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?

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.

I have a similar problem too but in the case of my Panasonic TH-42PX80B Plasma the only way to get the 100hz image smoothing to work is if the refresh rate is set to 50hz, if it gets 60hz from the PC then the 100hz is disabled and the picture tears really badly. Now I've set the PC to 50hz by forcing the Vsync in the ATI drivers I've cured the tearing but now i get the jitters in slow panning shots.

mdaria510 Wrote: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.

I have a plasma display, at 48Hz. Just tried Atlantis beta 2 with Planet Earth pans... terrible results. Unusable for me. It judders like crazy and, by looking at the infos (I) one can see that the framerate fluctuates wildly, even if no frames are dropped.

I suggest developers give a long look at Reclock.

Alright, I'm now 100% convinced this is an issue with refresh rates. I have the option to set my TV to a 24hz refresh rate in 1080p. Ran a few tests:

1) Playing a 24p source (720 planet earth .mkv) at a 24hz refresh rate eliminates the judder. There's one frame per refresh, and XBMC doesnt seem to have any issue syncing them.

However, leaving the HTPC on at 24hz is hardly practical, and I'd suspect that 99% of HTPC users don't have a TV that can run at anything but 60hz.

As soon as I switched the refresh rate back to 60hz, the jitter is back.

Next, I tried some 30fps (progressive) video - mostly videogame trailers. I was hoping that since 30hz is a multiple of 60hz, it would play back in sync. Didnt happen - same deal, microjitters, but no dropped frames. It did appear to be slightly better, able to lock the interpolation for a second or two here or there, but it still didnt play back right.

Tried all of the above videos, 24p/30p in media player classic, and they played back smooth as butter, and all locked perfectly to the interpolation due to the proper 2:2 and 3:2 cadences.

Tried all in 480p, 720p and 1080p to see if the video card was being choked - exact same behavior despite the resolution.

So as far as I can tell, unless the frame rate of the video is exactly the same as the refresh rate, the video does not play back at the proper rate. This may be only a windows specific problem - I have no way of telling otherwise, but there is definitely a major issue here.

This is still a beta, so bugs are expected, but I dont feel that it should be brought out of beta until this is taken care of. I'm not sure exactly how to help the devs reproduce the problem, but from seeing the responses in this thread, I'm clearly not the only one experiencing this.

ashlar Wrote:I have a plasma display, at 48Hz. Just tried Atlantis beta 2 with Planet Earth pans... terrible results. Unusable for me. It judders like crazy and, by looking at the infos (I) one can see that the framerate fluctuates wildly, even if no frames are dropped.

I suggest developers give a long look at Reclock.

Give it a try at 24hz (if you can), and see what happens.

I use the linux port on my htpc but after reading this thread i tried the windows port. I can confirm the video on windows is considerably more juddier. I think this issue might effect the linux port aswell though because video smoothness has definatly suffered due to a recent change (pre beta1). I tried planet earth 720p on both platforms, panning is watchable on linux but not perfect. On windows its unwatchable.

Maybe im just noticing it more now im looking for it (linux) but i do think there is a problem. Just my 2.

cheers