Starting from Android 4.1 (Jelly Bean), developers are able to use MediaPlayer APIs to accomplish the Closed Captioning feature. On Android Lollipop, a lot of changes went in MediaPlayer, specifically related to Closed Captioning. Some apps have issues using subtitles and Closed Captioning on Android Lollipop, with subtitles showing up sporadically or not at all. Some change logs related to MediaPlayer and Closed Captioning: https://android.googlesource.com/platform/frameworks/base/+/3cdf7c5%5E!/ https://android.googlesource.com/platform/frameworks/base/+/8c4d53c%5E!/
Exoplayer detection is probably the best suggestion on Android Lollipop which should solve the issue. Subtitle interface for ExoPlayer: http://google.github.io/ExoPlayer/doc/reference/com/google/android/exoplayer/text/Subtitle.html. Please check Amazon Lollipop KB article “Android 5.0 adds Exoplayer as a more flexible and extendible media player (https://forums.developer.amazon.com/forums/thread.jspa?threadID=4892&tstart=0 )” for more information on Exoplayer.
Keywords: MediaPlayer, ExoPlayer, Lollipop, Closed Captioning