Are you saying you have attempted partial-upgrades?
That is unsupported. Dont do it.
Yeah I guess so. However you are trying to do these partial-upgrades .. stop.
To whatever extent you may be successfull .. being partially upgraded is equal to broken.
As to which multimedia package .. use ffmpeg.
As to the conflict .. this is from verrryyy old news.
Essentially we will just use the better package manager and point at the one you want.
sudo pacman -Syu jre-openjdk
(I have no idea if you actually want jre or jdk, but if you dont do java programming yourself then probably you just want jre-openjdk .. or even jre-openjdk-headless, which is what I have installed)
If that also produces error then please copy the output here.