Just realized my previous patch doesn't work quite right.  I uploaded a better
sample file that actually has visible captions to /incoming/hevc_cc.ts.  I
tested with that file doing hevc->x264 and it works.

This is basically an exact copy of the existing h264 logic.
Signed-off-by: Will Kelleher <wkelleher@gogoair.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>