Would you expalin more detail about problem on FireTV?
Problem is common for all Android based Set Top Boxes (FireTV, old GoogleTV, recently announced Android TV, etc.) - they don't have touch interface.
These devices use remote controlls ...
Please add to API ability to pass additional audio streams for video file in similar way as it done for subtitles.
sample: I have on server mp4 video file with 1 audio stram and couple mp3 files with audio in other languages.