lavu: add helper functions for integer lists.

Add av_int_list_length() to compute a list length.
Add av_opt_set_int_list() to set a binary option.

Signed-off-by: Nicolas George <nicolas.george@normalesup.org>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
lavfi/buffersink: accept parameters as options.

Move validation from init to query_formats().
Accept the formats lists as binary options.

Signed-off-by: Nicolas George <nicolas.george@normalesup.org>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
ffmpeg: use options for abuffersink.

Also remove unused buffersink_params.

Signed-off-by: Nicolas George <nicolas.george@normalesup.org>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avfilter: remove mixed args hack for scale.

Our option handling code does not need this hack.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>