It appears that not all Apple implementations follow the HLS guidelines.
While the DEFAULT=NO for an audio track should be optional and default
to NO, in practice native HLS players Safari and iOS devices treat the
missing DEFAULT as a MAYBE.
Fixes#1169
Legacy players, e.g. older versions of ExoPlayer, do not handle default webvtt text alignment correctly. Need to specify `align:center` explicitly cues without text alignment for backwards compatibility.
Fixes#925.
This changes the default MP4 output to use TTML and adds a way to
choose which one is used. This is done with 'format=ttml+mp4' or
'format=vtt+mp4'.
This also fixes the boxes output in WebVTT in MP4.
Change-Id: Ieaa7fc44fbf4dc020a5bb70cfa3578ec10e088ce
Mark Sargent
Joey Parrish
Vishal Shah
Jacob Trimble