Android 25 added support for i-frame-interval to be a floating
point value. Store the property as a float and use the newer
version when it's available.
Android 19 added an API for dynamically changing the bitrate in a running
codec.
Also make it so that even when not update-able at runtime, parameters will at least
be stored so that they take effect the next the codec is restarted.
gst_amc_color_format_copy will copy in/out a frame resides at a
GstAmcBuffer. Lots of codes in gst_amc_video_*_fill_buffer are moved to
this new function.