Add "mixed_refs" description suggested by Loren Merritt and update accompanying

comment in the code.

Originally committed as revision 7235 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/avcodec.h

@@ -365,7 +365,7 @@ typedef struct RcOverride{
 #define CODEC_FLAG2_LOCAL_HEADER  0x00000008 ///< place global headers at every keyframe instead of in extradata
 #define CODEC_FLAG2_BPYRAMID      0x00000010 ///< H.264 allow b-frames to be used as references
 #define CODEC_FLAG2_WPRED         0x00000020 ///< H.264 weighted biprediction for b-frames
-#define CODEC_FLAG2_MIXED_REFS    0x00000040 ///< H.264 multiple references per partition
+#define CODEC_FLAG2_MIXED_REFS    0x00000040 ///< H.264 one reference per partition, as opposed to one reference per macroblock
 #define CODEC_FLAG2_8X8DCT        0x00000080 ///< H.264 high profile 8x8 transform
 #define CODEC_FLAG2_FASTPSKIP     0x00000100 ///< H.264 fast pskip
 #define CODEC_FLAG2_AUD           0x00000200 ///< H.264 access unit delimiters

libavcodec/utils.c

@@ -696,7 +696,7 @@ static const AVOption options[]={
 {"directpred", "direct mv prediction mode - 0 (none), 1 (spatial), 2 (temporal)", OFFSET(directpred), FF_OPT_TYPE_INT, 2, INT_MIN, INT_MAX, V|E},
 {"bpyramid", "allows B-frames to be used as references for predicting", 0, FF_OPT_TYPE_CONST, CODEC_FLAG2_BPYRAMID, INT_MIN, INT_MAX, V|E, "flags2"},
 {"wpred", "weighted biprediction for b-frames (H.264)", 0, FF_OPT_TYPE_CONST, CODEC_FLAG2_WPRED, INT_MIN, INT_MAX, V|E, "flags2"},
-{"mixed_refs", NULL, 0, FF_OPT_TYPE_CONST, CODEC_FLAG2_MIXED_REFS, INT_MIN, INT_MAX, V|E, "flags2"},
+{"mixed_refs", "one reference per partition, as opposed to one reference per macroblock", 0, FF_OPT_TYPE_CONST, CODEC_FLAG2_MIXED_REFS, INT_MIN, INT_MAX, V|E, "flags2"},
 {"8x8dct", "high profile 8x8 transform (H.264)", 0, FF_OPT_TYPE_CONST, CODEC_FLAG2_8X8DCT, INT_MIN, INT_MAX, V|E, "flags2"},
 {"fastpskip", "fast pskip (H.264)", 0, FF_OPT_TYPE_CONST, CODEC_FLAG2_FASTPSKIP, INT_MIN, INT_MAX, V|E, "flags2"},
 {"aud", "access unit delimiters (H.264)", 0, FF_OPT_TYPE_CONST, CODEC_FLAG2_AUD, INT_MIN, INT_MAX, V|E, "flags2"},