Inconsistent quality sharing video files

[ydraw]

I am using the Share Screen > Advanced > Video function to share a range of mp4 files of differing lengths and file sizes. All are set to 1920 x 1080. Sometimes the video plays fine, other times it takes ages to buffer, sometimes the quality is so low you can't read any text in the video. Once the quality has dropped this low it will stay there and videos that had previously been shared in the same meeting and were crystal clear will now also be low quality. Ending the meeting and restarting it will reset the quality. 

Have tried multiple devices, speed tests, different number of participants in the meeting, different internet connections, different files and can't work out what is causing it to sometimes have such poor quality. I need to find a way to share mp4 files with reliable consistency. 

Is there something I can do to the video files themselves? A setting in Zoom? Help?