AVFilterPad起一个输入和输出接口的作用

结构体

/*** A filter pad used for either input or output.*/
struct AVFilterPad {/*** Pad name. The name is unique among inputs and among outputs, but an* input may have the same name as an output. This may be NULL if this* pad has no need to ever be referenced by name.*/const char *name;/*** AVFilterPad type.*/enum AVMediaType type;/*** The filter expects writable frames from its input link,* duplicating data buffers if needed.** input pads only.*/
#define AVFILTERPAD_FLAG_NEEDS_WRITABLE                  (1 << 0)/*** The pad's name is allocated and should be freed generically.*/
#define AVFILTERPAD_FLAG_FREE_NAME                       (1 << 1)/*** A combination of AVFILTERPAD_FLAG_* flags.*/int flags;/*** Callback functions to get a video/audio buffers. If NULL,* the filter system will use ff_default_get_video_buffer() for video* and ff_default_get_audio_buffer() for audio.** The state of the union is determined by type.** Input pads only.*/union {AVFrame *(*video)(AVFilterLink *link, int w, int h);AVFrame *(*audio)(AVFilterLink *link, int nb_samples);} get_buffer;/*** Filtering callback. This is where a filter receives a frame with* audio/video data and should do its processing.** Input pads only.** @return >= 0 on success, a negative AVERROR on error. This function* must ensure that frame is properly unreferenced on error if it* hasn't been passed on to another filter.*/int (*filter_frame)(AVFilterLink *link, AVFrame *frame);/*** Frame request callback. A call to this should result in some progress* towards producing output over the given link. This should return zero* on success, and another value on error.** Output pads only.*/int (*request_frame)(AVFilterLink *link);/*** Link configuration callback.** For output pads, this should set the link properties such as* width/height. This should NOT set the format property - that is* negotiated between filters by the filter system using the* query_formats() callback before this function is called.** For input pads, this should check the properties of the link, and update* the filter's internal state as necessary.** For both input and output filters, this should return zero on success,* and another value on error.*/int (*config_props)(AVFilterLink *link);
};

函数

/*** Get the name of an AVFilterPad.** @param pads an array of AVFilterPads* @param pad_idx index of the pad in the array; it is the caller's*                responsibility to ensure the index is valid** @return name of the pad_idx'th pad in pads*/
const char *avfilter_pad_get_name(const AVFilterPad *pads, int pad_idx);/*** Get the type of an AVFilterPad.** @param pads an array of AVFilterPads* @param pad_idx index of the pad in the array; it is the caller's*                responsibility to ensure the index is valid** @return type of the pad_idx'th pad in pads*/
enum AVMediaType avfilter_pad_get_type(const AVFilterPad *pads, int pad_idx);

/*** Append a new input/output pad to the filter's list of such pads.** The *_free_name versions will set the AVFILTERPAD_FLAG_FREE_NAME flag* ensuring that the name will be freed generically (even on insertion error).*/
int ff_append_inpad (AVFilterContext *f, AVFilterPad *p);
int ff_append_outpad(AVFilterContext *f, AVFilterPad *p);
int ff_append_inpad_free_name (AVFilterContext *f, AVFilterPad *p);
int ff_append_outpad_free_name(AVFilterContext *f, AVFilterPad *p);