QtAV is deprecated https://www.qtav.org/blog/new-sdk.html
I wrote QtAV when I knew nothing about multimedia, so the framework is not well designed. The new framework MDK is better at any aspect.
About the new MDK SDK
Why Binary SDK only?
It save lives of both users and me. Users do not have to waste times in building the code, fixing build error, and runtime errors caused by error build.
Most users just use a library, but are not able to contribute
Open Source?
No, at least not for all users. But some modules and dependencies will be. For example MFT decoder, Android utilities.