func: static int init_input(AVFormatContext *s,const char *filename,AVDictionary **options) if ( s -> pb )  s -> flags |= 0x80; if ( ! s -> iformat )  return av_probe_input_buffer ( s -> pb , & s -> iformat , filename , s , 0 , s -> probesize ) ; int av_probe_input_buffer(AVIOContext *pb,AVInputFormat **fmt,const char *filename,void *logctx,unsigned int offset,unsigned int max_probe_size) uint8_t * mime_type ; if ( ! max_probe_size )  max_probe_size = ( 1 << 20 ); if ( max_probe_size > ( 1 << 20 ) )  max_probe_size = ( 1 << 20 ); if ( max_probe_size < 2048 )  if ( offset >= max_probe_size )  if ( ! ( * fmt ) && pb -> av_class && av_opt_get ( pb , "mime_type" , 0x1 , & mime_type ) >= 0 && mime_type )  if ( ! av_strcasecmp ( mime_type , "audio/aacp" ) )  * fmt = av_find_input_format ( "aac" ); AVInputFormat *av_find_input_format(const char *short_name) AVInputFormat * fmt = ( ( void * ) 0 ) ; while ( fmt = av_iformat_next ( fmt ) )  if ( match_format ( short_name , fmt -> name ) )  static int match_format(const char *name,const char *names) int namelen ; if ( ! name || ! names )  namelen = ( strlen ( name ) ); len = ( ( p - names > namelen ? p - names : namelen ) ); if ( ! av_strncasecmp ( name , names , len ) )  