[Luke Cage]

@Spiderfish
Yes, InputStream Adaptive will be required for bitrate switching, but it is currently not available at this time (no ETA).
Currently you only have a few manual options,
1. In the YouTube add-on settings enable 'Settings - General - Always ask for the video quality' and choose what is appropriate for your connection at the time.
2. In the InputStream Adaptive settings set 'Settings - General - Max. Resolution general decoder' to '720p'
3. In the InputStream Adaptive settings set ' Settings - General - Stream Selection' to 'Manual' and choose the quality during playback from the OSD 'Settings - Video Settings - Video stream'

 Thanks for your tips it's mitigate the issue some how better than before 

Although those were all mentioned to you earlier, and not deemed worthy enough. >:/
One of them you yourself proposed to another member as a solution to his/her issue.>:/

 Thanks for your tips it's mitigate the issue some how better than before 

So what was before, and is now better mitigated?: >:/

I noticed that when the internet speed is high the video running smoothly and no issue but when the internet speed is slow then the video start breaking and audio scattering! but how can I prevent this problem even if the internet speed is low...

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I came back to your request and today during troubleshooting my issue I got something will help you with your request, go to settings/general and chose Always ask for the video quality and enable it then every video will ask you for quality and you can choose only audio for what video you want! I think it's fair enough for you 

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@Spiderfish
To me it looks connection related from the log, which you seem to have confirmed this already with #1,417. 
Bitrate switching in InputStream Adaptive is not currently implemented, but for now setting 'Max. Resolution general decoder' to 720p may help.

@Luke Cage 
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My asking is..I s there any option I can make it working upon internet speed,,,for example if internet speed low then choose 240p and if internet speed high choose 1080p ? I think this will reduce the issue of mine! because I am using 4G connection not fiber and sometimes the internet speed is reduce so can I achieve that with youtube addon?

I tried to enable choose quality enabled then I tried to choose it manually! but I need it automatically upon internet speed provided!

Press the green button for that to happen.