"Adjust Display Refresh Rate" vs "Sync Playback to Display"

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hydraSlav Offline
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Question  "Adjust Display Refresh Rate" vs "Sync Playback to Display"
Post: #1
I've been struggling to understand this one:
http://kodi.wiki/view/Settings/Videos

"Adjust Display Refresh Rate" and "Sync Playback to Display".
To my understanding:
- The first one changes the TV refresh rate (Hz) to match video (FPS).
- The second one changes the video speed (FPS) to match the TV (Hz).

To my understanding, that is mutually exclusive, yet the settings page allows both to be enabled.
The wiki does not mention anything about one setting overriding the other.

So can someone please explain how they can co-exist?\

Thank you
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Ned Scott Offline
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Post: #2
It should be mutually exclusive in theory. I'm not entirely sure myself, but a guess would be that if the TV refresh rate can't be changed, then it falls back to changing the video FPS to match the current refresh rate?
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Memphiz Offline
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Post: #3
its not mutually exclusive - playing a 23.967fps movie with a tv which only supports 24hz will switch it to 24hz - sync to display will adapt for the rest

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(This post was last modified: 2015-03-02 15:29 by Memphiz.)
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noggin Online
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Post: #4
No - not mutually exclusive.

"Adjust Display Refresh Rate" will switch the output refresh rate when playing back a file to the best refresh rate that is supported by the display AND the hardware Kodi is running on (as reported by EDID) If you don't select this option then you output at a fixed display refresh rate, which is usually set in Settings->System->Video Output. This setting allows Kodi to change the frame rate of the video output fed to the display, to ensure the best refresh rate is selected.

So if you have a display that supports 50Hz and 60Hz content, 50Hz content will be output at 50Hz and 60Hz content at 60Hz, however 24Hz will be output at 60Hz with 3:2 (ignoring 1000/1001 refresh rates (*))
If you have a display that supports 24Hz, 50Hz and 60Hz content, then 24Hz will be output at 24H, 50Hz at 50Hz and 60Hz at 60Hz. This is great if you have a display and hardware that copes with everything flawlessly.

"Sync Playback to Display" is different. It alters the playback speed so that it matches the display refresh rate (which could be fixed or could be variable if you have also selected Adjust Display Refresh Rate)

Why is this useful?

Say you have a 50Hz display but 24p content. 24p content will look horrible if you play at 50Hz, but if you Sync Playback to Display it will play the 24Hz back at 25Hz which will look much nicer at 50Hz. (Even if you have a display that syncs to 60Hz and could watch 24p material with 3:2 - which is nicer - you may still chose to watch at 50Hz with speed up and 2:2 to avoid the 3:2 judder. I sometimes do.)

Also - if you have a Kodi platform that can't cope with 23.976Hz output, but it can cope with 24.000Hz, you would normally get a repeated frame every 40" or so to keep stuff in sync. However if you also select Sync Playback to Display then Kodi will slow speed up the 23.976Hz content to 24.000Hz - so no repeated frames (and thus no stutter) but you then have to sort the audio sync out (either by resampling or by dupe/dropping)

(*) 1000/1001 frame rates are the alternative 23.976 and 59.94 Hz rates that are actually used for a large proportion of so-called 24p and 60Hz content. This is because the first US colour TV standard, NTSC, required a slight change to the field refresh rate to avoid the line/field-locked colour subcarrier potentially interfering with the sound carrier used for broadcast audio. We've been cursed with it ever since - even with HDTV (which has to be refresh rate compatible with SDTV for downconversion purposes)
(This post was last modified: 2015-03-02 15:48 by noggin.)
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hydraSlav Offline
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Post: #5
Wow, thanks so much for detailed info.

So, in layman's terms:
Adjust Display Refresh Rate - big changes in refresh rate, if TV supports it.
Sync Playback to Display - small fine-tuning to be better matched to what TV has switched to.
So for best experience, if my hardware can do it, I should use both.

This only leaves the question of Audio. I've read that "resampling" doesn't work with passthrough, so it's either "dupe/drop" or "adjust audio clock" for me. I am having constant issue with audio being out of sync with video on my platform (Minix X8-H). Which option would provide better "sync'ness"?

Thank you.
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FernetMenta Online
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Post: #6
correct, "sync playback to display" makes no sense with passthrough audio. in general a/v sync is better with passthough disabled. but not sure if it does matter in your case. sorry to say but Android audio driver is a nightmare.
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hydraSlav Offline
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Post: #7
(2015-03-02 21:22)FernetMenta Wrote:  correct, "sync playback to display" makes no sense with passthrough audio.

Ahh, didn't realize that. So if I have passthrough, I should not enable "sync playback to display".

Thanks
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Ned Scott Offline
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Post: #8
Nice! I'll try to find a good spot on the wiki to deposit this info.
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nickr Offline
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Post: #9
Yes, preservation needed!

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J_Y_Mac Offline
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Post: #10
(2015-03-02 15:46)noggin Wrote:  Also - if you have a Kodi platform that can't cope with 23.976Hz output, but it can cope with 24.000Hz, you would normally get a repeated frame every 40" or so to keep stuff in sync.

What would that equate to using a time span of a 90 min bluray? I'm trying to decide on whether to enable Sync Playback to display. I've noticed that a/v sync is actually off by a little less when Sync Playback to Display is disabled. However, if I get a repeated frame too often I would rather just enable Sync Playback to Display, have a/v sync off by a little more, and duplicate or drop an audiopacket. I currently have a Samsung Plasma with Cinema Smooth 96hz enabled.

Also, if you could could you key me in what the different lines with letters stand for when looking at frames/second, a/v sync, ect.

My layout looks something like this with Sync Playback to Display disabled:

D
P

D
P

C
W

and with Sync Playback to Display enabled:

D
P

D
P

C
W
S

Thanks.
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fritsch Online
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Post: #11
Quote:I currently have a Samsung Plasma with Cinema Smooth 96hz enabled.

That's marketing bullshit. It alters the content the way it likes ... it cannot decide wether the input signal was meant to be 23.976 fps or was meant to be 24.0 or 60 hz when running at a wrong refreshrate ... it tries to interpolate the signal it gets - if that sucks - it will even suck more. Just disable it.

The letters are described in detail in our wiki

Edit: If you did not find the link: Codecinfo (wiki)

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(This post was last modified: 2015-03-05 09:34 by fritsch.)
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J_Y_Mac Offline
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Post: #12
(2015-03-05 09:34)fritsch Wrote:  
Quote:I currently have a Samsung Plasma with Cinema Smooth 96hz enabled.

That's marketing bullshit. It alters the content the way it likes ... it cannot decide wether the input signal was meant to be 23.976 fps or was meant to be 24.0 or 60 hz when running at a wrong refreshrate ... it tries to interpolate the signal it gets - if that sucks - it will even suck more. Just disable it.

The letters are described in detail in our wiki

Edit: If you did not find the link: Codecinfo (wiki)

I appreciate the feedback and the link. Now I've got some experimenting to do and I know exactly what I'm looking at. Thanks again.
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voochi Offline
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Post: #13
(2015-03-02 21:22)FernetMenta Wrote:  correct, "sync playback to display" makes no sense with passthrough audio.

If it made no sense then the option would not be available.

It makes no sense if there is a big mismatch in display refreshrate and video framerate. For example 24p content on a 50Hz display.

But if they are very close - for example if the video is 24Hz but the display only supports 23.976Hz - then it is quite acceptable to use "sync playback to display (dupe/drop)". The % of duped or dropped packets in this example is so small that it should be completely inaudible.
(This post was last modified: 2015-03-17 17:40 by voochi.)
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Theron Offline
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Post: #14
Yes, it does. If you alter the video but pass through the audio to your receiver, they will be out of sync. That option only works right when all the signal processing is done together.
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Theron Offline
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Post: #15
(2015-03-05 09:34)fritsch Wrote:  
Quote:I currently have a Samsung Plasma with Cinema Smooth 96hz enabled.

That's marketing bullshit. It alters the content the way it likes ... it cannot decide wether the input signal was meant to be 23.976 fps or was meant to be 24.0 or 60 hz when running at a wrong refreshrate ... it tries to interpolate the signal it gets - if that sucks - it will even suck more. Just disable it.

The letters are described in detail in our wiki

Edit: If you did not find the link: Codecinfo (wiki)

I don't have a Samsung display, but my Panasonic plasmas correctly repeat 24p frames at 96Hz without interpolation AFAIK.
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