Users can't make anything with its content.
Making it opaque might allow us to avoid one level of indirection.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
According to its documentation it returns "pts of the last muxed packet
+ its duration", but the value it actually returns right now is
(possibly guessed) dts after muxer-internal bitstream filtering (if
any).
This function was added for ffmpeg.c, but it is not used there anymore.
Since the value it returns is ill-defined and so inappropriate for any
serious use, deprecate it.
