why ExoPlayer doesn't work on old devices with android API lower than 23?

it took quite a few days to realize that something wrong is going on with old devices with API lower than 23 and I searched intensively but without an answer. So when I found my answer I thought that it's worth sharing with the community

I used multiple emulator versions but the weird thing is that some devices couldn't either load the video (sudden stop) or it loads it till showing the thumbnail and it freezes, so the answer is basically that nothing is wrong with ExoPlayer, it's just the emulator that cannot play the media with an emulator with lower API than 23 due to a decoder issue but mainly on a usual use ExoPlayer will function properly with android devices of 16+ API. you can check the DOCUMENTATION for more details.

It might be late,but hope help someone.
Excerpt from ExoPlayer Doc. Some Android emulators do not properly implement components of Android’s media stack, and as a result do not support ExoPlayer. This is an issue with the emulator, not with ExoPlayer. Android’s official emulator (“Virtual Devices” in Android Studio) supports ExoPlayer provided the system image has an API level of at least 23. System images with earlier API levels do not support ExoPlayer. The level of support provided by third party emulators varies. Issues running ExoPlayer on third party emulators should be reported to the developer of the emulator rather than to the ExoPlayer team. Where possible, we recommend testing media applications on physical devices rather than emulators.