Not familiar with Rockchip. Plenty of searches come up with cases of people incorporating ffmpeg into Rockchip projects. I still see the license files and headers. What is different with this DMCA takedown?

https://github.com/nyanmisaka/ffmpeg-rockchip

The one you reference doesn't look like it misrepresents the licenses, i.e. of you use it to make your own derivative you would expect to have to share modifications you make to the LGPL code.