avconv: update -map option help text

avconv.c

@@ -4113,7 +4113,7 @@ static const OptionDef options[] = {
     { "c", HAS_ARG | OPT_STRING | OPT_SPEC, {.off = OFFSET(codec_names)}, "codec name", "codec" },
     { "codec", HAS_ARG | OPT_STRING | OPT_SPEC, {.off = OFFSET(codec_names)}, "codec name", "codec" },
     { "pre", HAS_ARG | OPT_STRING | OPT_SPEC, {.off = OFFSET(presets)}, "preset name", "preset" },
-    { "map", HAS_ARG | OPT_EXPERT | OPT_FUNC2, {(void*)opt_map}, "set input stream mapping", "file.stream[:syncfile.syncstream]" },
+    { "map", HAS_ARG | OPT_EXPERT | OPT_FUNC2, {(void*)opt_map}, "set input stream mapping", "[-]input_file_id[:stream_specifier][,sync_file_id[:stream_specifier]]" },
     { "map_metadata", HAS_ARG | OPT_EXPERT | OPT_FUNC2, {(void*)opt_map_metadata}, "set metadata information of outfile from infile",
       "outfile[,metadata]:infile[,metadata]" },
     { "map_chapters",  OPT_INT | HAS_ARG | OPT_EXPERT | OPT_OFFSET, {.off = OFFSET(chapters_input_file)},  "set chapters mapping", "input_file_index" },