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audio sync at 24fps


lifespeed

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Guest asrequested

--audio-delay=<sec>

Audio delay in seconds (positive or negative float value). Positive values delay the audio, and negative values delay the video.

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lifespeed

It sounds realistic to implement given frame rate switching used to be part of Emby.  I guess it is a matter of priority.

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So what you're saying is we need multiple audio delay settings, each corresponding to different framerates?

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lifespeed

So what you're saying is we need multiple audio delay settings, each corresponding to different framerates?

 

The simplest implementation would just be an adjustment for 24fps, and no adjustment for 60fps.  I am afraid I can't speak to any requirements for PAL and 25fps as I have a television spec'd for the USA.

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Jdiesel

PMP has a setting in the config file for audio offset for 24hz videos and a offset for all refreshrates expect 24hz. Ideally you would have some type of in app adjust to fine tune in real time if needed as a standard offset doesn't always apply to all files. Audio sync is real messy bussiness. 

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lifespeed

and by 24fps you really mean 23.976 right?

Yes, it is really 23.976.

 

Edit: and 60fps is really 59.94 if I remember correctly.

Edited by lifespeed
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puithove

technically it'd need to be for both 23.976 & 24 as the AVR processes them the same way.  As far as I know it's the same also for 25.  So probably should be if refresh rate > 23 and <= 25, then apply this audio delay.  Else, apply this audio delay (0 by default).

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puithove

But make them adjustable since it's highly variable between different hardware.  that way if the default delay doesn't work for someone, they can adjust it to fit their needs.

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lifespeed

So what you're saying is we need multiple audio delay settings, each corresponding to different framerates?

The adjustable delay implemented in the latest 2.7.9 beta fixes the 24fps audio sync problem.  I set it to 167ms and the audio sync is spot on, thanks!

 

Interestingly, 4/24 =0.167, and your typical 120Hz television interpolates 4 extra frames for every single frame of 24Hz content (120/24=5).  I don't think 167ms is a coincidence, and is probably a good default value for most hardware.

 

Video smoothness is so much better letting the TV interpolate to 120Hz, vs whatever 3:2 pulldown craziness MPV player does to "match" to 60Hz.

Edited by lifespeed
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  • 2 months later...
lifespeed

I hate to ask you to revisit this, but there is a problem lumping 23-24fps (really 23.976) together with 25fps.  Due to the reality of NTSC and PAL being on different continents, NTSC TVs only support 24fps, rarely both 24 and 25fps.  25fps does not play well at 24fps, causing an annoying jump in the video every few seconds.  The reality is that 25fps must be played at 60fps on an NTSC TV here in North America.

 

So what does this mean for this much-appreciated audio sync fix?  25fps video played at 60fps needs a different audio delay, in my case typically zero.  I think the simplest and most appropriate fix is to just offer a separate delay for 23-24 fps and 25fps.  Otherwise the wrong delay gets applied for 25fps PAL content played on an NTSC TV, an all-too-common occurrence.

 

Thanks again for addressing this issue.

Edited by lifespeed
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  • 1 month later...
lifespeed

The fix for the audio sync issue is to *only* apply optional delay to those refresh rates in the 23 - 25fps range that are configured in automatic refresh rate switching.  For example, a north american Emby user will only have 23;24 configured as valid automatic refresh rates.  For your typical TV that does not support 25fps, this content is best played at 60fps and won't apply optional audio delay.  Therefore, the audio delay will not be inappropriately applied to 25fps played back at 60fps by respecting the automatic refresh rate configuration.

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  • 1 year later...
pcubillos

So, in reading this topic, I have not seen a fix for the lip sync issue. I am having this problem in my MKV video that I have encoded with RipBot264. The video's work fine in VLC and Media Portal. Appreciate if someone could advise on a fix if i missed it. Thanks!!!

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So, in reading this topic, I have not seen a fix for the lip sync issue. I am having this problem in my MKV video that I have encoded with RipBot264. The video's work fine in VLC and Media Portal. Appreciate if someone could advise on a fix if i missed it. Thanks!!!

 

Hi there, have you explored the audio delay options in the app?

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