lavfi/buffersink: add a summary documentation of the API.

libavfilter/buffersink.h

@@ -31,6 +31,42 @@
  * @defgroup lavfi_buffersink Buffer sink API
  * @ingroup lavfi
  * @{
+ *
+ * The buffersink and abuffersink filters are there to connect filter graphs
+ * to applications. They have a single input, connected to the graph, and no
+ * output. Frames must be extracted using av_buffersink_get_frame() or
+ * av_buffersink_get_samples().
+ *
+ * The format negotiated by the graph during configuration can be obtained
+ * using the accessor functions:
+ * - av_buffersink_get_time_base(),
+ * - av_buffersink_get_format(),
+ * - av_buffersink_get_frame_rate(),
+ * - av_buffersink_get_w(),
+ * - av_buffersink_get_h(),
+ * - av_buffersink_get_sample_aspect_ratio(),
+ * - av_buffersink_get_channels(),
+ * - av_buffersink_get_channel_layout(),
+ * - av_buffersink_get_sample_rate().
+ *
+ * The format can be constrained by setting options, using av_opt_set() and
+ * related functions with the AV_OPT_SEARCH_CHILDREN flag.
+ *  - pix_fmts (int list),
+ *  - sample_fmts (int list),
+ *  - sample_rates (int list),
+ *  - channel_layouts (int64_t),
+ *  - channel_counts (int list),
+ *  - all_channel_counts (bool).
+ * Most of these options are of type binary, and should be set using
+ * av_opt_set_int_list() or av_opt_set_bin(). If they are not set, all
+ * corresponding formats are accepted.
+ *
+ * As a special case, if neither channel_layouts nor channel_counts is set,
+ * all valid channel layouts are accepted, but channel counts without a
+ * layout are not, unless all_channel_counts is set.
+ * Also, channel_layouts must not contain a channel layout already accepted
+ * by a value in channel_counts; for example, if channel_counts contains 2,
+ * then channel_layouts must not contain stereo.
  */
 
 /**