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robl45 · 2011-08-19, 21:21

a while back there was a thread about the issues on 24FPS audio being out of sync. I narrowed it down to being XVID files that are the issue as H264 works flawlessly. Was wondering if this was ever fixed? I know people say you can set the audio delay back like .250 or something, but that never works very well for me, makes it barely watchable and thats about it.

**steelman1991** · 2011-08-20, 00:47

Wasn't just XVID files - in my case it was all files with a fps other than 25/50fps. Still not resolved as far as I am aware.

robl45 · 2011-08-26, 20:36

steelman1991 Wrote:Wasn't just XVID files - in my case it was all files with a fps other than 25/50fps. Still not resolved as far as I am aware.

hmm, for me h264 and x264 play fine, its just xvid files and only 24p ones. everything else is great, sure wish there was a fix though as even doing the audio stuff, it still works like crap.

**jubilex** · (This post was last modified: 2012-02-14, 20:21 by jubilex.)

This one is baffling to me. Aside from what would seem to be the importance of a media player being able to play audio and video in sync, I mean.

How does it happen that playing 24fps content on a 24fps display results in out of sync audio? I mean, shouldn't this be much EASIER for the system to do? How on earth does converting a 24fps video on the fly to 60fps not result in loss of sync, but simply playing the video at its native framerate does?

I am talking about h264 mkvs here, some with DTS audio, some with AC3.

robl45 · 2012-02-14, 20:09

If you play 24p at 60hz you will have jutter and unnatural motion. So audio being in sync is the least of the worries,I just use mpc-hc now as external player

**jubilex** · 2012-02-14, 21:40

24fps at 60hz has judder, but that's not a processing issue, it's just a fact of turning 24 frames into 60.

Audio sync when playing 24fps on a 24hz display is inexplicable to me. Can someone explain to me why the audio would go out of sync when matching the source to the display?

robl45 · 2012-02-14, 23:21

jubilex Wrote:24fps at 60hz has judder, but that's not a processing issue, it's just a fact of turning 24 frames into 60.

Audio sync when playing 24fps on a 24hz display is inexplicable to me. Can someone explain to me why the audio would go out of sync when matching the source to the display?

exactly, so discussing 60hz with good audio sync is useless as the video will be horrible. as it was explained to me in another thread, xbmc won't sync correctly if the refresh rates match, you would need to use a multiple of the refresh rate which is not feasible for most people. then the sync to display should work properly.

at any rate, it doesn't appear like the issue will ever be fixed. part of the reason is it seems xbmc is grabbing the refresh rate from directdraw instead of direct3d which appears to give a more correct refresh rate. in another thread, code was posted to change it to see if it worked better, but no one actually changed it and thats beyond my skills.

DDDamian · 2012-02-14, 23:30

jubilex Wrote:How does it happen that playing 24fps content on a 24fps display results in out of sync audio?

A lot has to do with the fact that 24p is really 23.976 (fps*(1000/1001)) an issue that goes back to early NTSC specifications and lingers to this day. Most GPU's don't quite nail that obscure number, some being far better than others, but none perfect.

You can slave to the video clock and garble audio or slave to the audio clock and garble video, or upgrade your GPU - those are your practical choices if you notice the issue.

For very course issues (like being out 200msec) there has been a patch floating around for a while allowing you to adjust the audio delay depending on the video frequency. Search for Global AV Delay.

**jubilex** · 2012-02-15, 02:15

DDDamian Wrote:A lot has to do with the fact that 24p is really 23.976 (fps*(1000/1001)) an issue that goes back to early NTSC specifications and lingers to this day. Most GPU's don't quite nail that obscure number, some being far better than others, but none perfect.

But then why would they be better at converting 23.976 to 60hz?

Quote:You can slave to the video clock and garble audio or slave to the audio clock and garble video, or upgrade your GPU - those are your practical choices if you notice the issue.

GPU is an Nvidia 560ti. Is there a list somewhere of what GPUs can do this?

Quote:For very course issues (like being out 200msec) there has been a patch floating around for a while allowing you to adjust the audio delay depending on the video frequency. Search for Global AV Delay.

Hmm, I'll check this out, thanks. From what I remember last time I tried this, though, the sync was never a consistent x milliseconds off at every point in the video.

DDDamian · 2012-02-15, 02:30

jubilex Wrote:But then why would they be better at converting 23.976 to 60hz?

Resampling it to a higher framerate does mask it better,

jubilex Wrote:GPU is an Nvidia 560ti. Is there a list somewhere of what GPUs can do this?.

Here's a good review. I have an ATI 6450 that is almost bang-on.

jubilex Wrote:Hmm, I'll check this out, thanks. From what I remember last time I tried this, though, the sync was never a consistent x milliseconds off at every point in the video.

Many users report seeing a constant 200-259msec delay with 24p material - the patch will only help you if that's the case. If it's just sporadic frame drops the GPU is the culprit.

Here's a build I did which will play back HD audio and allows you a global delay, but you'll have to get specifics on the delay setup from it's thread.

**jubilex** · 2012-02-15, 04:01

Thanks for all the suggestions. Having briefly tried 24fps playback (it seems to work with some files), it's really hard to go back to jittery pans.

robl45 · 2012-02-15, 14:17

no you can't because that doesn't work with xbmc, at best it works on some films and not others, some films it doesn't work at all, others it works until it stops working and then you have to hit play/pause over and over again until the missed counter stops going up and then watch your movie with the on screen display on to see if the missed counter started moving again.

DDDamian Wrote:You can slave to the video clock and garble audio or slave to the audio clock and garble video, or upgrade your GPU - those are your practical choices if you notice the issue.

**ashlar** · 2012-02-15, 15:08

DDDamian Wrote:A lot has to do with the fact that 24p is really 23.976 (fps*(1000/1001)) an issue that goes back to early NTSC specifications and lingers to this day. Most GPU's don't quite nail that obscure number, some being far better than others, but none perfect.

I think there's a bit of confusion here. The problem you are describing doesn't make audio go out of sync. It results in a dropped frame once in a while (depending on how far you are from 23.976; I am at 23.97620 and it would happen once every 5 minutes if my calculations are not off). The delay on 24p material comes from something else. Otherwise it would affect all media players equally and, instead, it's XBMC only.

robl45 · 2012-02-15, 16:00

ashlar Wrote:I think there's a bit of confusion here. The problem you are describing doesn't make audio go out of sync. It results in a dropped frame once in a while (depending on how far you are from 23.976; I am at 23.97620 and it would happen once every 5 minutes if my calculations are not off). The delay on 24p material comes from something else. Otherwise it would affect all media players equally and, instead, it's XBMC only.

true it is hard to determine, I believe part of it is xbmc reads from directdraw so regardless of whether your hz is set at 23.9762, it still thinks its at 24hz. hence if you look at the OSD, you should notice speed at +.100 instead of .000 like it should be if reading it correctly.

second, its not syncing correctly when using sync to display. so for me on .AVI files, the missed counter will never stop and it never gets sync and audio and video are off sync. on h264/x264 type of containers, it sometimes will sync up on the missed counter right away, other times it takes a few tries of pause play to get it to sync up. then it usually works, well until it starts missing again and this can happen right in the middle of a movie. plus every time you might pause the movie, you have to bring up the OSD to make sure when you hit play, the missed counter isn't increasing, otherwise you have to hit pause and play over and over until you lock on.

its definately an xbmc problem, but unfortunately, it doesn't seem like it will ever be fixed.

DDDamian · 2012-02-15, 16:08

ashlar Wrote:I think there's a bit of confusion here. The problem you are describing doesn't make audio go out of sync. It results in a dropped frame once in a while (depending on how far you are from 23.976; I am at 23.97620 and it would happen once every 5 minutes if my calculations are not off). The delay on 24p material comes from something else. Otherwise it would affect all media players equally and, instead, it's XBMC only.

Hi Ashlar - that's why I distinguished between the odd dropped frame and course offsets of ~200ms a few posts back Rolleyes