av_guess_codec   3033 ffmpeg.c                   codec_id = av_guess_codec(oc->oformat, NULL, oc->filename, NULL, CODEC_TYPE_VIDEO);
av_guess_codec   3168 ffmpeg.c                   codec_id = av_guess_codec(oc->oformat, NULL, oc->filename, NULL, CODEC_TYPE_AUDIO);
av_guess_codec    764 libavformat/avformat.h enum CodecID av_guess_codec(AVOutputFormat *fmt, const char *short_name,