HLS: Don't expose CEA-608 track when CLOSED-CAPTIONS=NONE

[rileymacdonald]

I'm upgrading from ExoPlayer r.1.5.9 to r2.2.0. Quick question:

ExoPlayer.EventListener.onTracksChanged() is returning a TrackGroup with a single Format with a sampleMimeType of application/cea-608 during video load. I assume the content I'm loading doesn't have cea608 captions due to the following master.m3u8 response:

#EXT-X-STREAM-INF:PROGRAM-ID=1,BANDWIDTH=2195000,RESOLUTION=960x540,CODECS="avc1.77.30, mp4a.40.2",CLOSED-CAPTIONS=NONE

What's the best way to verify my video content doesn't have cea608 captions present?