Flavor Selector and Prefered Flavor Bitrate
Flavor selection criteria
There are several factors that influence initial bitrate selection and whether "auto" adaptive bitrate can be enabled or not.
You can see the flavor selection logic in code here.
Basically the flow is as follows:
1) Filters playable sources,
2) Filters via playable adaptive streaming source where adaptive streaming is active.( DASH, HLS, SmoothStreaming or HDS)
The preferred bitrate will be passed into the adaptive stream initial flavor logic.
3) User selected or player configured preferred bitrate is used to select nearest target.
4) A subset of flavors are defined that don't need a plugin to be played.
5) A flavor matching the embed size of the player is selected against flavor subset.
6) If no native playback flavors was selected, the first compatible flavor is selected.