Now text-based WebVTT also uses the generic media pipeline. This
converts the WebVttTextOutputHandler to a WebVttMuxer to be more
consistent with the other muxer types.
This also allows choosing between single-segment text and multi-segment.
Before, we would generate both and use single-segment for DASH and
multi-segment for HLS; but now you can choose between either and either
are supported in both DASH and HLS.
Change-Id: I6f7edda09e01b5f40e819290d3fe6e88677018d9
Now the same pipeline for handling the audio/videos streams will handle
the segmented text streams too. This doesn't apply to the text output,
only to the MP4 variants. This also fixes a bug where we added the
X-TIMESTAMP-MAP tag even when there wasn't TS streams; this doesn't
otherwise change the behavior around that tag.
Change-Id: I03f7cea56efa42e96311c00841330629a14aa053