Missing legend in ffmpeg full help page

Solution 1:

Legend

E.......... = Encoding or Muxing
.D......... = Decoding or Demuxing
..F........ = Filtering
...V....... = Video
....A...... = Audio
.....S..... = Subtitle
......X.... = Export
.......R... = Readonly
........B.. = Bitstream Filter
.........T. = Runtime (Indicates which filters support the `enable` option)
..........P = Deprecated

Source code reference

In libavutil/opt.c:

av_log(av_log_obj, AV_LOG_INFO, "%c", (opt->flags & AV_OPT_FLAG_ENCODING_PARAM) ? 'E' : '.');
av_log(av_log_obj, AV_LOG_INFO, "%c", (opt->flags & AV_OPT_FLAG_DECODING_PARAM) ? 'D' : '.');
av_log(av_log_obj, AV_LOG_INFO, "%c", (opt->flags & AV_OPT_FLAG_FILTERING_PARAM)? 'F' : '.');
av_log(av_log_obj, AV_LOG_INFO, "%c", (opt->flags & AV_OPT_FLAG_VIDEO_PARAM   ) ? 'V' : '.');
av_log(av_log_obj, AV_LOG_INFO, "%c", (opt->flags & AV_OPT_FLAG_AUDIO_PARAM   ) ? 'A' : '.');
av_log(av_log_obj, AV_LOG_INFO, "%c", (opt->flags & AV_OPT_FLAG_SUBTITLE_PARAM) ? 'S' : '.');
av_log(av_log_obj, AV_LOG_INFO, "%c", (opt->flags & AV_OPT_FLAG_EXPORT)     ? 'X' : '.');
av_log(av_log_obj, AV_LOG_INFO, "%c", (opt->flags & AV_OPT_FLAG_READONLY)       ? 'R' : '.');
av_log(av_log_obj, AV_LOG_INFO, "%c", (opt->flags & AV_OPT_FLAG_BSF_PARAM)      ? 'B' : '.');
av_log(av_log_obj, AV_LOG_INFO, "%c", (opt->flags & AV_OPT_FLAG_RUNTIME_PARAM)  ? 'T' : '.');
av_log(av_log_obj, AV_LOG_INFO, "%c", (opt->flags & AV_OPT_FLAG_DEPRECATED)     ? 'P' : '.');

In libavutil/opt.h:

#define AV_OPT_FLAG_ENCODING_PARAM  1   ///< a generic parameter which can be set by the user for muxing or encoding
#define AV_OPT_FLAG_DECODING_PARAM  2   ///< a generic parameter which can be set by the user for demuxing or decoding
#define AV_OPT_FLAG_AUDIO_PARAM     8
#define AV_OPT_FLAG_VIDEO_PARAM     16
#define AV_OPT_FLAG_SUBTITLE_PARAM  32
/**
 * The option is intended for exporting values to the caller.
 */
#define AV_OPT_FLAG_EXPORT          64
/**
 * The option may not be set through the AVOptions API, only read.
 * This flag only makes sense when AV_OPT_FLAG_EXPORT is also set.
 */
#define AV_OPT_FLAG_READONLY        128
#define AV_OPT_FLAG_BSF_PARAM       (1<<8) ///< a generic parameter which can be set by the user for bit stream filtering
#define AV_OPT_FLAG_RUNTIME_PARAM   (1<<15) ///< a generic parameter which can be set by the user at runtime
#define AV_OPT_FLAG_FILTERING_PARAM (1<<16) ///< a generic parameter which can be set by the user for filtering
#define AV_OPT_FLAG_DEPRECATED      (1<<17) ///< set if option is deprecated, users should refer to AVOption.help text for more information
#define AV_OPT_FLAG_CHILD_CONSTS    (1<<18) ///< set if option constants can also reside in child objects