Brave browser is Chromium-based, and Chromium-based browsers recently went through some problems playing videos (I don't know about embedded media) due to incompatibilities between the latest versions of Chromium and certain versions of ffmpeg (the codec library used for video playback).
I recently had to go through a bunch of steps to get videos working again in Opera (which is also based on Chromium) on my wife's Android device for this reason, and on my MX Linux laptop. Then, when the Android device was ready for an OS/platform update, I uninstalled what I'd done (which "unfixed" the videos), did the update, and, hey presto, the videos were working after the update (so I guess they figured out the problem and made the fix part of their update).
Since you haven't said what version of Brave you're on, what the smartphone is, whether it's Android, what version of Android, etc., obviously I can't know that your situation is the same as what we dealt with. (And although they're both Chromium-based, Brave and Opera are different.)
Still, I'd look into the possibility of a fix involving using a different version of ffmpeg...or else, getting the latest update either for Brave, or for your smartphone's system, if you haven't already.