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>

doc/filters.texi

@@ -1768,9 +1768,10 @@ Below is a description of the currently available audio sinks.
 Buffer audio frames, and make them available to the end of filter chain.
 
 This sink is mainly intended for programmatic use, in particular
-through the interface defined in @file{libavfilter/buffersink.h}.
+through the interface defined in @file{libavfilter/buffersink.h}
+or the options system.
 
-It requires a pointer to an AVABufferSinkContext structure, which
+It accepts a pointer to an AVABufferSinkContext structure, which
 defines the incoming buffers' formats, to be passed as the opaque
 parameter to @code{avfilter_init_filter} for initialization.
 
@@ -1780,13 +1781,6 @@ Null audio sink, do absolutely nothing with the input audio. It is
 mainly useful as a template and to be employed in analysis / debugging
 tools.
 
-@section abuffersink
-This sink is intended for programmatic use. Frames that arrive on this sink can
-be retrieved by the calling program using the interface defined in
-@file{libavfilter/buffersink.h}.
-
-This filter accepts no parameters.
-
 @c man end AUDIO SINKS
 
 @chapter Video Filters
@@ -6298,12 +6292,12 @@ Buffer video frames, and make them available to the end of the filter
 graph.
 
 This sink is mainly intended for a programmatic use, in particular
-through the interface defined in @file{libavfilter/buffersink.h}.
+through the interface defined in @file{libavfilter/buffersink.h}
+or the options system.
 
-It does not require a string parameter in input, but you need to
-specify a pointer to a list of supported pixel formats terminated by
--1 in the opaque parameter provided to @code{avfilter_init_filter}
-when initializing this sink.
+It accepts a pointer to an AVBufferSinkContext structure, which
+defines the incoming buffers' formats, to be passed as the opaque
+parameter to @code{avfilter_init_filter} for initialization.
 
 @section nullsink