Muxer flv [FLV (Flash Video)]:
    Common extensions: flv.
    Mime type: video/x-flv.
    Default video codec: flv1.
    Default audio codec: mp3.
flv muxer AVOptions:
  -flvflags          <flags>      E........ FLV muxer flags (default 0)
     aac_seq_header_detect              E........ Put AAC sequence header based on stream data
     no_sequence_end              E........ disable sequence end for FLV
     no_metadata                  E........ disable metadata for FLV
     no_duration_filesize              E........ disable duration and filesize zero value metadata for FLV
     add_keyframe_index              E........ Add keyframe index metadata


