av_log_set_callback 3490 ffmpeg.c           av_log_set_callback(log_callback_help);
av_log_set_callback 4509 ffserver.c             av_log_set_callback(http_av_log);
av_log_set_callback  127 libavutil/log.h void av_log_set_callback(void (*)(void*, int, const char*, va_list));