Libav, for some reason, merged this as a public API function. This will
aid in future merges.
A define is left for backwards compat, just in case some person
used it, since it is in a public header.
Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>
In particular, add support for t, pos, n, r parameters, and add an eval
mode option.
Also, partially reword option documentation.
With several major edit by Stefano Sabatini.
Signed-off-by: Stefano Sabatini <stefasab@gmail.com>