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
c
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
c
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
c
/**
* 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
c
/**
* 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
c
/**
* 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);