The changes to source caching in #5156 introduced a regression where the source options were no longer available to plugins. This PR makes sure the cached source object retains any source options passed along.
SourceHandlers that use MSE have a problem: if they push a segment into a SourceBuffer and then seek close to the end, playback will stall and/or there will be a massive downswitch in quality. The general approach to fixing this that was discussed on slack was by setting the playback rate of the player to zero, buffering all that was required, and then restoring the previous playback rate. In my implementation, I've done this in the source handler (see: videojs/videojs-contrib-hls#1374).
From the video.js perspective, it should ensure that the UI reflects the buffering status and that the player API behaves like you'd expect -- that is to say, that it will fire seeking immediately after a call to currentTime, and it will fire seeked, canplay, canplaythrough, and playing when everything is buffered.
Chuck Wilson