[Kodi20/21] Video stuttering with subtitles on less powerful android devices.

My final opinion for users here~!!! (https://github.com/xbmc/xbmc/issues/21554#issuecomment-1404578671)

Bug report

Describe the bug

Here is a clear and concise description of what the problem is:

Sorry for my ENG.

Intermittent frequent video micro stuttering when text based subtitles(not image based) are visible on my amazon fire stick 4k max.

Since the introduction of the new subtitle renderer in Kodi20, I've used only shield tv pro 2019 so I have not reailized the stuttering until I bought fire stick 4k max recently. The moment the subtitles appear, the stuttering appears very briefly.

I tried to resolve the stuttering by changing settings(adjust display refresh rate, sync playback to display, dirty region, smartredraw, etc...), but didn't work.

Only lowering GUI resolution limit to "720" (The default setting, Auto, is probably set at 1080 resolution) was helpful to decrease the incidence of the stuttering, but the micro stuttering was not completely gone. On the contrary, setting GUI resolution limit to "unlimited" on 4K display worsened the stuttering causing frame drop.

Not as bad as fire stick, but shield tv pro also has the stuttering with 1080 GUI resolution and if set to 2160(unlimited), getting worse. If turn off the subtitles, butter smooth playback.

Expected Behavior

Here is a clear and concise description of what was expected to happen:

Video playback should be smooth without micro stuttering when subtitles are visible like Kodi19. Video playback was smooth in Kodi19, regardless of GUI resolution.

Actual Behavior

Video stuttering when subtitles are visible.

Possible Fix

I don't know.

To Reproduce

Steps to reproduce the behavior:

1. Prepare 4K sample videos. I picked 4K sample videos from official kodi wiki(https://kodi.wiki/view/Samples). 4K number 15(https://mega.nz/file/af4zSAbQ#gBiHRiX3oLnBvxMNnytC08v8DRkKzQIkhGpg96nAWXE) and number 16(https://mega.nz/file/nehDka6Z#C5_OPbSZkONdOp1jRmc09C9-viDc3zMj8ZHruHcWKyA).
2. Make text based srt subtitles with some lines for test. for video 15 HDR10Plus_PA_DTSX.zip for video 16 HDR10Plus_PB_EAC3JOC.zip
3. Play sample test videos on suitable android devices and enable test subtitles.
4. Watch for micro stuttering carefully. (Turn off any motion smoothing adjust function of your TV before test)
5. Change GUI resolution limit setting from 720 to unlimited and restart Kodi to apply. Observe the stuttering changes depending on GUI resolution. The sample videos are too short so you may not notice the micro stuttering when GUI resolution is set to 720. But I'm sure you can reproduce the micro stuttering with 4K TV shows such as The Boys or WeCrashed, etc...

Debuglog

The debuglog can be found here: kodi.log

Screenshots

Here are some links or screenshots to help explain the problem:

Additional context or screenshots (if appropriate)

Here is some additional context or explanation that might help:

Amazon fire stick 4k max is a relatively recent device and the benchmark score is good. So I hope to use Kodi20 without stuttering on this device. If I'm wrong, plz let me know what I'm missing. Thank you.

Your Environment

Used Operating system:

• Android

• iOS

• tvOS

• Linux

• OSX

• Windows

• Windows UWP

• Operating system version/name: android 9, 11

• Kodi version: Kodi 20 nexus

note: Once the issue is made we require you to update it with new information or Kodi versions should that be required. Team Kodi will consider your problem report however, we will not make any promises the problem will be solved.