clear out currentSource on loadstart

[gkatsev]

Starting with v5.2.2 we've been returning the cached src for source handlers. This is important for techs that end up using MSE so that we return an the original source rather than the blob url that gets set.
However, there are cases when, in the html5 tech, the underlying video element could get a new video set, bypassing the videojs API. We want to actually pick up this change to return the new sources.

[gkatsev]

The main question: should we dispose the current source handler?

[dmlap]

Sounds good to me.

[gkatsev]

Also, loadstartlintener should probably be moved to a private prototype method so that removing it works correctly on subsequent calls to setSrc.

[gkatsev]

Opening it up now for discussion. This should get tests but I'll wait off till we decide the specific functionality.
@videojs/core-committers opinions? Thanks.

[gkatsev]

(Also, the direct issue that sprouted this has been worked around for now, so, it's not a huge hurry)

[chemoish]

I haven't been following, but is this currentSource similar to #2678?

[gkatsev]

@chemoish sort of, actually. The Source Handler interface in videojs (what videojs-contrib-hls uses) gives the source ({src, type}) obj to the source handler to work on. It'll then cache it locally for the life of that source handler. The issue is that we keep returning that cached value even when the underlying video src has been changed because it didn't go through the videojs API (we didn't know it changed).

[chemoish]

I understand the error, but didn't quite follow if the existing currentSource_ implementation (#2833) makes #2678 obsolete.

#2678 doesn't handle anything other than attempting to store unmodified sources for MSE reasons.

(So regardless, the issue that this PR is addressing still must be addressed)

[gkatsev]

Ah, I see. No, it doesn't necessarily make it obsolete. #2833 made it so that currentSrc would now return the cached source in the case of MSE. It only returns the source url and not the type as well.
So, with MSE, and #2833 you would now get http://example.com/video.m3u8 instead of blob://example.com when calling player.currentSrc().
#2678 probably needs to get updated to use currentSource_. That feature could still be useful since it returns both the type and source of the video. currentSource_ is the source object (what you pass to player.src() that is given to Source Handlers.