ffmpeg: mark sseof as an input-only option

doc/ffmpeg.texi

@@ -508,7 +508,7 @@ input until the timestamps reach @var{position}.
 @var{position} must be a time duration specification,
 see @ref{time duration syntax,,the Time duration section in the ffmpeg-utils(1) manual,ffmpeg-utils}.
 
-@item -sseof @var{position} (@emph{input/output})
+@item -sseof @var{position} (@emph{input})
 
 Like the @code{-ss} option but relative to the "end of file". That is negative
 values are earlier in the file, 0 is at EOF.

fftools/ffmpeg_opt.c

@@ -3340,7 +3340,7 @@ const OptionDef options[] = {
                         OPT_INPUT | OPT_OUTPUT,                      { .off = OFFSET(start_time) },
         "set the start time offset", "time_off" },
     { "sseof",          HAS_ARG | OPT_TIME | OPT_OFFSET |
-                        OPT_INPUT | OPT_OUTPUT,                      { .off = OFFSET(start_time_eof) },
+                        OPT_INPUT,                                   { .off = OFFSET(start_time_eof) },
         "set the start time offset relative to EOF", "time_off" },
     { "seek_timestamp", HAS_ARG | OPT_INT | OPT_OFFSET |
                         OPT_INPUT,                                   { .off = OFFSET(seek_timestamp) },