[DomesticMachine]

UPDATE: Found a solution to the problem: de- & remuxing the problematic MKV files seems to do the trick!

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(I found some existing threads about similar problems with DTS playback and dropped frames, but that's not strictly speaking the case here, so I was bold enough to think this might be a separate problem and started a new topic. )

I recently encountered a couple of movies that suffer from an uneven/jittery/varying framerate, but only when I play them with the DTS audio track. However, not a single frame is dropped, the framerate just doesn't stay constant.

At first I wasn't sure if this was just the normal "24fps on 60Hz" effect and I'm imagining the whole thing, but then I realized the FPS display in the CodecInfo window backs up my observations: Normally, when watching a 24fps movie, it stays at 23.98 most of the time, sometimes jumping momentarily to 23.95 or 24.00. However, with the "problem" movies, the FPS indicator constantly travels between 22-25 FPS, and while you can watch the movie for a moment without noticing anything strange, you'll eventually notice a small but annoying jerk here and there.

This only seems to happen with _some_ movies with a DTS track - I have many movies with the same audio and video format as the problem movies (h264 1080p DTS), and they play just fine. But in any case, it seems DTS is what causes the problem: one of the problem movies has both an AC3 and DTS track, and as soon as I switch to AC3, FPS goes to almost static 23.98. Switch back to DTS, and the "guess the FPS" show begins.

I have tested this on two different Win7 PC's with different hardware, and XBMC 10.1 and the latest nightly build. I have tried changing pretty much all playback settings in XBMC, no effect. The only thing that seems to help is to check "Adjust display refresh rate to match video", but that causes some other problems (like my TV delaying the picture so that audio goes out of sync), so I'd rather leave it unchecked if only possible.

I also tried playing the same movies with VLC. Without the FPS display (is there a similar thing in VLC?) it's hard to be 100% sure, but I _think_ VLC doesn't have the same kind of jitter.

Any ideas? :confused2:

[MrSkyline]

what soundcard do you have? and how is it connected to your speaker setup?

And this is just a wild guess, but you never know, did you try it with vsync enabled in the XBMC settings?

[DomesticMachine]

what soundcard do you have? and how is it connected to your speaker setup?

Both PCs have an integrated soundcard. The other PC is an Asus EEEbox (Atom/ION) with an optical connection to my amplifier. And the other is my desktop PC with a Realtek sound chip and analog 5.1 connection to speakers. I also tried changing XBMC's audio output settings (Analog/Optical/Coax), and disabled "DTS capable receiver" so that XBMC did not even send the DTS stream to the amplifier - no effect.

And this is just a wild guess, but you never know, did you try it with vsync enabled in the XBMC settings?

Yep, I always have vsync enabled.

[MrSkyline]

both have realtek chipsets, i've had problems with DTS and onboard realtek chipsets in the past, it might help to use an alternative soundcard because DTS is allot of data for a soundcard to handle, and the realtek chip might be influencing the speed of other components.
An alternative soundcard has its own dedicated chip that can handle the audio rendering, leaving enough computing power for the video part.

Also make sure you have the latest audio drivers, maybe that helps. (http://www.realtek.com/downloads/)

[DomesticMachine]

both have realtek chipsets, i've had problems with DTS and onboard realtek chipsets in the past, it might help to use an alternative soundcard because DTS is allot of data for a soundcard to handle, and the realtek chip might be influencing the speed of other components.
An alternative soundcard has its own dedicated chip that can handle the audio rendering, leaving enough computing power for the video part.

Thanks for the tips, but I don't think Realtek is to blame here. I switched XBMC's audio output to HDMI, which doesn't work for some reason (XBMC says "failed to initialize audio device"), but if I understand correctly, that also means XBMC is not outputting anything thru the Realtek chip (at least I'm not hearing anything). Still, the same problem persists - DTS in some movies = jitter, DTS in some other movies = fine, AC3 = fine.

[MrSkyline]

when using HDMI for audio, you use the soundcard intergraded in the graphics card.
This is a seperate soundcard, you can set it as your main audio device in windows by richt-clicking the speaker icon in the botom right of the screen and selecting playback devices, set HDMI to default, and set XBMC to default.
If that doesn't work then i'm out of ideas i think :p

[DomesticMachine]

when using HDMI for audio, you use the soundcard intergraded in the graphics card.
This is a seperate soundcard, you can set it as your main audio device in windows by richt-clicking the speaker icon in the botom right of the screen and selecting playback devices, set HDMI to default, and set XBMC to default.
If that doesn't work then i'm out of ideas i think :p

Thanks again, but HDMI not working wasn't really a problem, it just proved that audio hardware probably isn't what causes the original DTS jitter problem.

Anyway, I tried XBMC on my MacBook Pro, and guess what, the exactly same DTS jitter problem happens there. I guess this is something deep in the XBMC code, and not related to hardware in any way. Next I'll try to dig a little deeper into the problem movies themselves and see if there's any particular aspect in their format that causes the problem (and even if it could be fixed somehow).

UPDATE: Well, seems like de- and remuxing a problematic MKV file might do the trick. At least it did for one of the three movies that had this problem. I have never done de/remuxing before, but it was surprisingly easy.

[WillemB]

Mind telling which tooling you use? Have some jitter in some movies too

[gabbott]

Mind telling which tooling you use? Have some jitter in some movies too

The best multi-platform tool for a job like that is mkvmerge


http://www.bunkus.org/videotools/mkvtoolnix/