RPI4 on Libreelec 9.1.502 (also on 9.2) subtitles cause playback to skip frame or 2

    Hi all,

    Although its already being mentioned on other thread , i preferred creating new thread because i believe i have good examples to reproduce the problem easily.

    Playback is just fine when subtitles are off (talking about text one , simple srt file)

    But when subtitles are on , it seems there is frame skip(s) every time subtitle is shown (not while it displayed).

    I have some test judder videos which i created a dummy subtitles for them (they are audio-less so audio output problem is out of the equation)

    They are downloadable from https://drive.google.com/drive/folders/1ewxril7331dlillggkfnlkcg8qwrtxc1 (also uploaded 1 zip of single frame rate movie here)

    There is a file for each frame rate (23.976-59.940) , the srt files have the same content just different filename.

    When playing back the file you can notice :

    1.First time subtitles is show (text is "line 1") there is a frame skip (i think this problem also happened on previous libreelec/rpi)

    2.When "line 1" is removed , no problem.

    3.Now , when "line 2" is shown there is again a frame skip , but since "line 3" and "line 4" are shown with a 1 second wait , it seems there is no frame skip.

    4."line 5" comes after a longer break , so again a frame skip and so does "line 7".

    In my setup , the skips are most noticeable on the 59.940 file (highest frame rate) but can be noticed also on the lower ones (30.0 and 25.0 seems to be harder to spot).

    Please note that in order to check the files properly you need

    1.Enable change refresh rate on playback start (so 24fps file will be used under 24p resolution)

    2.Disable any motion interpolation/compensation on your TV/monitor if you have any enabled (Generally i don't recommend using it :))

    Hope this help in fixing this issue.

    Please let me know if anything else is needed.

    Kodi 18.5 is out.

    One of the highlights is "Fixes to external subtitle playback".

    Maybe it could be a fix for the problem , tough on RPI3B with 18.4 i don't have any of the above problems.

    Hoping to see it fixed on next LE version.:)

    Just installed LE 9.2.

    Problem still persist on RPI4 :(

    Installed 9.2 also on my RPI3B2 , no skips on low fps movies , but the 59.994 fps is not working on 9.2 , it worked just fine on 9.0.X (playback just freeze after 2-3 seconds).

    Damn, that's bad news. I'll install 9.2 in the evening nevertheless...
    I know subtitles aren't first priority or maybe it's a complicated problem, but I hope for the hearing-impaired that this will be fixed with the next release. Or better: For the people who live with hearing-impaired a la "don't you dare turning the ST off, you ignorant egocentric" (which would be me).... ;)

    Just to make things clear, Indeed subtitles can used also for hearing-impaired , but its also massively being used for people which English is not their native tongue.

    I for instance mainly use english subtitles although the audio is in english rather than using my language subtitles because i don't get anything loose in translation and learn few words/phrases from time time :).

    But most non english speakers must have subtitles in order to be able to watch a something and understand it.

    "Change refresh rate on playback start" is required when you want to match monitor refresh rate to the played file FPS.

    23.976 fps video is best played when monitor refresh rate is 23.976 hz.

    25.000 fps video is best played when monitor refresh rate is 25/50 hz and so on.

    Without this , smooth playback is not possible.

    New TV sets has motion interpolation feature , which adds frame in between , so 23.976 fps gets few frames generated to fit the refresh rate of the TV.

    This results in non "normal" video playback , motion looks like a video game rater than a real movie, this is the reason i mentioned to disable it so frame skip would be

    Ok, I have to test the settings better.

    Thanks for explanation…

    P.S.

    After testing some vídeos with this function on and off, there is really a difference in image quality, i had already commented on another topic that felt some difference in image quality compared to another source playing the same vídeo file and now i see where did that come from...

    Edited once, last by maxi (November 28, 2019 at 6:35 PM).

    No update since 9.2 and problem still persist of course.

    Its less noticeable when video "always" show subtitles (non stop dialog for example) or when there is almost no dialog.

    It appears a frame skip happens only when subtitles "turned on" , IE video has no subtitles and then a dialog starts then subtitles are shown (frame skip) if following subtitles overlap previous ones (or close to that) there is no frame skip , if subtitles removed from screen and then after 1-3 seconds are shown there is a frame skip.

    In the attached test files i generated subtitles files to make this clear and consistent and easy to reproduce.

    I hope this got resolved soon or at least noticed by some developer , since its quite a big issue .

    Well , i am quite sure its not a Kodi problem but a Libreelec since its happens only on RPI4 , On RPI3 i got no problems with Libreelec 9.2.

    But i guess it would not hurt to post it also there.

    Hi everyone ,

    It seems 9.2.1 really improves this issue.

    On 30 fps , 29.94 fps , 25 fps samples , playback seems perfect with subtitles.


    60 fps sample cant really be played on this version with or without subtitles , not sure why , it starts fine but then starts to stutter badly , other 60 fps videos i checked works fine.

    on 23.976/24 fps , playback seems better , but still on samples videos there is slight stutter (more like micro stutter) comparing to non subtitles playback , on "real videos" it seems o.k , still checking...