Improve option description.

Originally committed as revision 7276 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/utils.c

@@ -556,7 +556,7 @@ static const AVOption options[]={
 {"p_mask", "inter masking", OFFSET(p_masking), FF_OPT_TYPE_FLOAT, 0, -FLT_MAX, FLT_MAX, V|E},
 {"dark_mask", "compresses dark areas stronger than medium ones", OFFSET(dark_masking), FF_OPT_TYPE_FLOAT, 0, -FLT_MAX, FLT_MAX, V|E},
 {"unused", NULL, OFFSET(unused), FF_OPT_TYPE_INT, DEFAULT, INT_MIN, INT_MAX},
-{"idct", "use inverse DCT", OFFSET(idct_algo), FF_OPT_TYPE_INT, DEFAULT, 0, INT_MAX, V|E|D, "idct"},
+{"idct", "select IDCT implementation", OFFSET(idct_algo), FF_OPT_TYPE_INT, DEFAULT, 0, INT_MAX, V|E|D, "idct"},
 {"auto", NULL, 0, FF_OPT_TYPE_CONST, FF_IDCT_AUTO, INT_MIN, INT_MAX, V|E|D, "idct"},
 {"int", NULL, 0, FF_OPT_TYPE_CONST, FF_IDCT_INT, INT_MIN, INT_MAX, V|E|D, "idct"},
 {"simple", NULL, 0, FF_OPT_TYPE_CONST, FF_IDCT_SIMPLE, INT_MIN, INT_MAX, V|E|D, "idct"},