/**
* Describe the class of an AVClass context structure. That is an //描述任意一个第一个指针指向AVClass的上下文结构体 * arbitrary struct of which the first field is a pointer to an * AVClass struct (e.g. AVCodecContext, AVFormatContext etc.). */ typedef struct AVClass { /** * The name of the class; usually it is the same name as the * context structure type to which the AVClass is associated. */ const char* class_name;/**
* A pointer to a function which returns the name of a context * instance ctx associated with the class. */ const char* (*item_name)(void* ctx); // 指向返回ctx指向的context实例的函数的指针/**
* a pointer to the first option specified in the class if any or NULL * * @see av_set_default_options() */ const struct AVOption *option; //指向在类中指向的第一个选项，没有则为NULL/**
* LIBAVUTIL_VERSION with which this structure was created. * This is used to allow fields to be added without requiring major * version bumps everywhere. */int version; //这个结构体是用那个版本的LIBAVUTIL_VERSION创建的
/**
* Offset in the structure where log_level_offset is stored. * 0 means there is no such variable */ int log_level_offset_offset;/**
* Offset in the structure where a pointer to the parent context for * logging is stored. For example a decoder could pass its AVCodecContext * to eval as such a parent context, which an av_log() implementation * could then leverage to display the parent context. * The offset can be NULL. */ int parent_log_context_offset;/**
* Return next AVOptions-enabled child or NULL */ void* (*child_next)(void *obj, void *prev);/**
* Return an AVClass corresponding to the next potential * AVOptions-enabled child. * * The difference between child_next and this is that * child_next iterates over _already existing_ objects, while * child_class_next iterates over _all possible_ children. */ const struct AVClass* (*child_class_next)(const struct AVClass *prev);/**
* Category used for visualization (like color) * This is only set if the category is equal for all objects using this class. * available since version (51 << 16 | 56 << 8 | 100) */ AVClassCategory category;/**
* Callback to return the category. * available since version (51 << 16 | 59 << 8 | 100) */ AVClassCategory (*get_category)(void* ctx);/**
* Callback to return the supported/allowed ranges. * available since version (52.12) */ int (*query_ranges)(struct AVOptionRanges **, void *obj, const char *key, int flags); } AVClass;