According to HLS spec: https://goo.gl/MiqjNd 4.3.4.1.1. Rendition Groups
- A Group MUST NOT have more than one member with a DEFAULT attribute of
YES.
- Each EXT-X-MEDIA tag with an AUTOSELECT=YES attribute SHOULD have a
combination of LANGUAGE[RFC5646], ASSOC-LANGUAGE, FORCED, and
CHARACTERISTICS attributes that is distinct from those of other
AUTOSELECT=YES members of its Group.
We tag the first rendition with a particular language in an audio group
with 'AUTOSELECT'; it is tagged with 'DEFAULT' too if the language
matches --default_language.
Fixes#315
Change-Id: Iacc0bc8c89ebffce8717fa65e82d6daf5a1f6adc
KongQun Yang