diff --git a/libavfilter/avfilter.h b/libavfilter/avfilter.h index 5717774098..b59e292e3e 100644 --- a/libavfilter/avfilter.h +++ b/libavfilter/avfilter.h @@ -412,20 +412,42 @@ enum AVMediaType avfilter_pad_get_type(const AVFilterPad *pads, int pad_idx); * callback functions used to interact with the filter. */ typedef struct AVFilter { - const char *name; ///< filter name + /** + * Filter name. Must be non-NULL and unique among filters. + */ + const char *name; /** - * A description for the filter. You should use the - * NULL_IF_CONFIG_SMALL() macro to define it. + * A description of the filter. May be NULL. + * + * You should use the NULL_IF_CONFIG_SMALL() macro to define it. */ const char *description; - const AVFilterPad *inputs; ///< NULL terminated list of inputs. NULL if none - const AVFilterPad *outputs; ///< NULL terminated list of outputs. NULL if none + /** + * List of inputs, terminated by a zeroed element. + * + * NULL if there are no (static) inputs. Instances of filters with + * AVFILTER_FLAG_DYNAMIC_INPUTS set may have more inputs than present in + * this list. + */ + const AVFilterPad *inputs; + /** + * List of outputs, terminated by a zeroed element. + * + * NULL if there are no (static) outputs. Instances of filters with + * AVFILTER_FLAG_DYNAMIC_OUTPUTS set may have more outputs than present in + * this list. + */ + const AVFilterPad *outputs; /** - * A class for the private data, used to access filter private - * AVOptions. + * A class for the private data, used to declare filter private AVOptions. + * This field is NULL for filters that do not declare any options. + * + * If this field is non-NULL, the first member of the filter private data + * must be a pointer to AVClass, which will be set by libavfilter generic + * code to this class. */ const AVClass *priv_class; @@ -443,29 +465,71 @@ typedef struct AVFilter { */ /** - * Filter initialization function. Called when all the options have been - * set. + * Filter initialization function. + * + * This callback will be called only once during the filter lifetime, after + * all the options have been set, but before links between filters are + * established and format negotiation is done. + * + * Basic filter initialization should be done here. Filters with dynamic + * inputs and/or outputs should create those inputs/outputs here based on + * provided options. No more changes to this filter's inputs/outputs can be + * done after this callback. + * + * This callback must not assume that the filter links exist or frame + * parameters are known. + * + * @ref AVFilter.uninit "uninit" is guaranteed to be called even if + * initialization fails, so this callback does not have to clean up on + * failure. + * + * @return 0 on success, a negative AVERROR on failure */ int (*init)(AVFilterContext *ctx); /** - * Should be set instead of init by the filters that want to pass a - * dictionary of AVOptions to nested contexts that are allocated in - * init. + * Should be set instead of @ref AVFilter.init "init" by the filters that + * want to pass a dictionary of AVOptions to nested contexts that are + * allocated during init. + * + * On return, the options dict should be freed and replaced with one that + * contains all the options which could not be processed by this filter (or + * with NULL if all the options were processed). + * + * Otherwise the semantics is the same as for @ref AVFilter.init "init". */ int (*init_dict)(AVFilterContext *ctx, AVDictionary **options); /** - * Filter uninitialization function. Should deallocate any memory held - * by the filter, release any buffer references, etc. This does not need - * to deallocate the AVFilterContext->priv memory itself. + * Filter uninitialization function. + * + * Called only once right before the filter is freed. Should deallocate any + * memory held by the filter, release any buffer references, etc. It does + * not need to deallocate the AVFilterContext.priv memory itself. + * + * This callback may be called even if @ref AVFilter.init "init" was not + * called or failed, so it must be prepared to handle such a situation. */ void (*uninit)(AVFilterContext *ctx); /** - * Queries formats supported by the filter and its pads, and sets the - * in_formats for links connected to its output pads, and out_formats - * for links connected to its input pads. + * Query formats supported by the filter on its inputs and outputs. + * + * This callback is called after the filter is initialized (so the inputs + * and outputs are fixed), shortly before the format negotiation. This + * callback may be called more than once. + * + * This callback must set AVFilterLink.out_formats on every input link and + * AVFilterLink.in_formats on every output link to a list of pixel/sample + * formats that the filter supports on that link. For audio links, this + * filter must also set @ref AVFilterLink.in_samplerates "in_samplerates" / + * @ref AVFilterLink.out_samplerates "out_samplerates" and + * @ref AVFilterLink.in_channel_layouts "in_channel_layouts" / + * @ref AVFilterLink.out_channel_layouts "out_channel_layouts" analogously. + * + * This callback may be NULL for filters with one input, in which case + * libavfilter assumes that it supports all input formats and preserves + * them on output. * * @return zero on success, a negative value corresponding to an * AVERROR code otherwise @@ -474,6 +538,10 @@ typedef struct AVFilter { int priv_size; ///< size of private data to allocate for the filter + /** + * Used by the filter registration system. Must not be touched by any other + * code. + */ struct AVFilter *next; } AVFilter;