avfilter_get_class 2692 ffmpeg_opt.c           show_help_children(avfilter_get_class(), AV_OPT_FLAG_VIDEO_PARAM | AV_OPT_FLAG_AUDIO_PARAM | AV_OPT_FLAG_FILTERING_PARAM);
avfilter_get_class 3743 ffplay.c           show_help_children(avfilter_get_class(), AV_OPT_FLAG_FILTERING_PARAM);
avfilter_get_class 1134 libavfilter/avfilter.h const AVClass *avfilter_get_class(void);