Android has its own media player APIs, you just have to tell it what to play and give it a place in the UI for the player canvas. You can even design your own controls for it.
When you open a webpage in Sync, that's an embedded web browser also provided by Android.
It's unlikely that Sync links to libwebp directly.
The Sync for Reddit app isn't usable anymore as it can no longer access the Reddit API. All you get are errors when you try to use it now.