Recommended Encoding Settings
https://support.video.ibm.com/hc/en-us/articles/207852117-Internet-connection-and-recommended-encoding-settings
1. For the greatest compatibility with a wide range of devices it is recommended to use -profile:v baseline -level 3.0
2. It is an idea to add -movflags +faststart if your file is going to be displayed online, with this setting it should start playback before fully downloaded
3. Use -pix_fmt yuv420p to allow playback on a wider range of devices
https://askubuntu.com/questions/734922/videos-which-are-converted-in-linux-do-not-play-in-mobile-browser