AMV bug workaround

Originally committed as revision 3099 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/avcodec.h

@@ -841,6 +841,7 @@ typedef struct AVCodecContext {
 #define FF_BUG_XVID_ILACE       4
 #define FF_BUG_UMP4             8
 #define FF_BUG_NO_PADDING       16
+#define FF_BUG_AMV              32
 #define FF_BUG_AC_VLC           0  ///< will be removed, libavcodec can now handle these non compliant files by default
 #define FF_BUG_QPEL_CHROMA      64
 #define FF_BUG_STD_QPEL         128

libavcodec/h263.c

@@ -3222,6 +3222,9 @@ static inline int get_amv(MpegEncContext *s, int n){
     int len = 1 << (s->f_code + 4);
     const int a= s->sprite_warping_accuracy;
     
+    if(s->workaround_bugs & FF_BUG_AMV)
+        len >>= s->quarter_sample;
+
     if(s->real_sprite_warping_points==1){
         if(s->divx_version==500 && s->divx_build==413)
             sum= s->sprite_offset[0][n] / (1<<(a - s->quarter_sample));