FFmpeg之AVFilterGraph

AVFilterGraph是对pileline的一个整体描述，没看之前以为里面大概是个有向无环图什么的来描述，进去一看，居然只是用链表来描述

结构体

先看结构体，主要关注里面的两个成员变量

AVFilterContext **filters;
   unsigned nb_filters;
AVFilterLink **sink_links;
    int sink_links_count;

以为avfilter是通过avFilterlink链接起来的，所以本质上来说只要有AVFilterLink就能描述清楚所有的链接图了

下面是全部定义

typedef struct AVFilterGraph {
    const AVClass *av_class;
    AVFilterContext **filters;
    unsigned nb_filters;

    char *scale_sws_opts; ///< sws options to use for the auto-inserted scale filters

    /**
     * Type of multithreading allowed for filters in this graph. A combination
     * of AVFILTER_THREAD_* flags.
     *
     * May be set by the caller at any point, the setting will apply to all
     * filters initialized after that. The default is allowing everything.
     *
     * When a filter in this graph is initialized, this field is combined using
     * bit AND with AVFilterContext.thread_type to get the final mask used for
     * determining allowed threading types. I.e. a threading type needs to be
     * set in both to be allowed.
     */
    int thread_type;

    /**
     * Maximum number of threads used by filters in this graph. May be set by
     * the caller before adding any filters to the filtergraph. Zero (the
     * default) means that the number of threads is determined automatically.
     */
    int nb_threads;

    /**
     * Opaque object for libavfilter internal use.
     */
    AVFilterGraphInternal *internal;

    /**
     * Opaque user data. May be set by the caller to an arbitrary value, e.g. to
     * be used from callbacks like @ref AVFilterGraph.execute.
     * Libavfilter will not touch this field in any way.
     */
    void *opaque;

    /**
     * This callback may be set by the caller immediately after allocating the
     * graph and before adding any filters to it, to provide a custom
     * multithreading implementation.
     *
     * If set, filters with slice threading capability will call this callback
     * to execute multiple jobs in parallel.
     *
     * If this field is left unset, libavfilter will use its internal
     * implementation, which may or may not be multithreaded depending on the
     * platform and build options.
     */
    avfilter_execute_func *execute;

    char *aresample_swr_opts; ///< swr options to use for the auto-inserted aresample filters, Access ONLY through AVOptions

    /**
     * Private fields
     *
     * The following fields are for internal use only.
     * Their type, offset, number and semantic can change without notice.
     */

    AVFilterLink **sink_links;
    int sink_links_count;

    unsigned disable_auto_convert;
} AVFilterGraph;

函数

/**
 * Allocate a filter graph.
 *
 * @return the allocated filter graph on success or NULL.
 */
AVFilterGraph *avfilter_graph_alloc(void);

/**
 * Create a new filter instance in a filter graph.
 *
 * @param graph graph in which the new filter will be used
 * @param filter the filter to create an instance of
 * @param name Name to give to the new instance (will be copied to
 *             AVFilterContext.name). This may be used by the caller to identify
 *             different filters, libavfilter itself assigns no semantics to
 *             this parameter. May be NULL.
 *
 * @return the context of the newly created filter instance (note that it is
 *         also retrievable directly through AVFilterGraph.filters or with
 *         avfilter_graph_get_filter()) on success or NULL on failure.
 */
AVFilterContext *avfilter_graph_alloc_filter(AVFilterGraph *graph,
                                             const AVFilter *filter,
                                             const char *name);

/**
 * Get a filter instance identified by instance name from graph.
 *
 * @param graph filter graph to search through.
 * @param name filter instance name (should be unique in the graph).
 * @return the pointer to the found filter instance or NULL if it
 * cannot be found.
 */
AVFilterContext *avfilter_graph_get_filter(AVFilterGraph *graph, const char *name);

/**
 * Create and add a filter instance into an existing graph.
 * The filter instance is created from the filter filt and inited
 * with the parameter args. opaque is currently ignored.
 *
 * In case of success put in *filt_ctx the pointer to the created
 * filter instance, otherwise set *filt_ctx to NULL.
 *
 * @param name the instance name to give to the created filter instance
 * @param graph_ctx the filter graph
 * @return a negative AVERROR error code in case of failure, a non
 * negative value otherwise
 */
int avfilter_graph_create_filter(AVFilterContext **filt_ctx, const AVFilter *filt,
                                 const char *name, const char *args, void *opaque,
                                 AVFilterGraph *graph_ctx);

/**
 * Enable or disable automatic format conversion inside the graph.
 *
 * Note that format conversion can still happen inside explicitly inserted
 * scale and aresample filters.
 *
 * @param flags  any of the AVFILTER_AUTO_CONVERT_* constants
 */
void avfilter_graph_set_auto_convert(AVFilterGraph *graph, unsigned flags);

enum {
    AVFILTER_AUTO_CONVERT_ALL  =  0, /**< all automatic conversions enabled */
    AVFILTER_AUTO_CONVERT_NONE = -1, /**< all automatic conversions disabled */
};

/**
 * Check validity and configure all the links and formats in the graph.
 *
 * @param graphctx the filter graph
 * @param log_ctx context used for logging
 * @return >= 0 in case of success, a negative AVERROR code otherwise
 */
int avfilter_graph_config(AVFilterGraph *graphctx, void *log_ctx);

/**
 * Free a graph, destroy its links, and set *graph to NULL.
 * If *graph is NULL, do nothing.
 */
void avfilter_graph_free(AVFilterGraph **graph);

dump一个图

/**
 * Dump a graph into a human-readable string representation.
 *
 * @param graph    the graph to dump
 * @param options  formatting options; currently ignored
 * @return  a string, or NULL in case of memory allocation failure;
 *          the string must be freed using av_free
 */
char *avfilter_graph_dump(AVFilterGraph *graph, const char *options);

解析一个图

图的解析分为三层，突然就忘了艹，总之就是先解析外边最大的block，再解析图内部的filter

/**
 * Add a graph described by a string to a graph.
 *
 * @note The caller must provide the lists of inputs and outputs,
 * which therefore must be known before calling the function.
 *
 * @note The inputs parameter describes inputs of the already existing
 * part of the graph; i.e. from the point of view of the newly created
 * part, they are outputs. Similarly the outputs parameter describes
 * outputs of the already existing filters, which are provided as
 * inputs to the parsed filters.
 *
 * @param graph   the filter graph where to link the parsed graph context
 * @param filters string to be parsed
 * @param inputs  linked list to the inputs of the graph
 * @param outputs linked list to the outputs of the graph
 * @return zero on success, a negative AVERROR code on error
 */
int avfilter_graph_parse(AVFilterGraph *graph, const char *filters,
                         AVFilterInOut *inputs, AVFilterInOut *outputs,
                         void *log_ctx);

/**
 * Add a graph described by a string to a graph.
 *
 * In the graph filters description, if the input label of the first
 * filter is not specified, "in" is assumed; if the output label of
 * the last filter is not specified, "out" is assumed.
 *
 * @param graph   the filter graph where to link the parsed graph context
 * @param filters string to be parsed
 * @param inputs  pointer to a linked list to the inputs of the graph, may be NULL.
 *                If non-NULL, *inputs is updated to contain the list of open inputs
 *                after the parsing, should be freed with avfilter_inout_free().
 * @param outputs pointer to a linked list to the outputs of the graph, may be NULL.
 *                If non-NULL, *outputs is updated to contain the list of open outputs
 *                after the parsing, should be freed with avfilter_inout_free().
 * @return non negative on success, a negative AVERROR code on error
 */
int avfilter_graph_parse_ptr(AVFilterGraph *graph, const char *filters,
                             AVFilterInOut **inputs, AVFilterInOut **outputs,
                             void *log_ctx);

/**
 * Add a graph described by a string to a graph.
 *
 * @param[in]  graph   the filter graph where to link the parsed graph context
 * @param[in]  filters string to be parsed
 * @param[out] inputs  a linked list of all free (unlinked) inputs of the
 *                     parsed graph will be returned here. It is to be freed
 *                     by the caller using avfilter_inout_free().
 * @param[out] outputs a linked list of all free (unlinked) outputs of the
 *                     parsed graph will be returned here. It is to be freed by the
 *                     caller using avfilter_inout_free().
 * @return zero on success, a negative AVERROR code on error
 *
 * @note This function returns the inputs and outputs that are left
 * unlinked after parsing the graph and the caller then deals with
 * them.
 * @note This function makes no reference whatsoever to already
 * existing parts of the graph and the inputs parameter will on return
 * contain inputs of the newly parsed part of the graph.  Analogously
 * the outputs parameter will contain outputs of the newly created
 * filters.
 */
int avfilter_graph_parse2(AVFilterGraph *graph, const char *filters,
                          AVFilterInOut **inputs,
                          AVFilterInOut **outputs);