What is the recommended DB, platform, and format for developing video sharing app?

[Cataster]

I am working on a project that is somewhat similar to the way Netflix works (as a streaming service), and have the following requirements:

• Database that stores video files
• Create group that can access the video
• Ability for Owner to invite/add users to the group(s)
• Video can be played/paused, and resumed if users close and come back to watch later.
• Users in the Group can watch the video at the same time
• Email/push notifications whenever owner of a group uploads a new video ready for watching

Now I have last developed in Android some 4 years ago, but in terms of cross platform compatibility, e.g. iOS and Android, what is the best approach for this project?

Should I use AWS or Azure to host the database? Would SQL database work well with storing videos? Is MP4 the best format considering its wide compatibility? From my android experience, I developed an App in Android studio, but is there a better alternative to develop an app that can work for both iOS and Android at once?