Add ff_h263_find_resync_marker() to find the bit position of the next resync_marker, if any.

patch by Gwenole Beauchesne gbeauchesne splitted-desktopcom
based on suggested implementation by me

Originally committed as revision 17560 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/h263.c

@@ -3292,6 +3292,27 @@ void ff_mpeg4_clean_buffers(MpegEncContext *s)
     s->last_mv[1][0][1]= 0;
 }
 
+/**
+ * finds the next resync_marker
+ * @param p pointer to buffer to scan
+ * @param end pointer to the end of the buffer
+ * @return pointer to the next resync_marker, or \p end if none was found
+ */
+const uint8_t *ff_h263_find_resync_marker(const uint8_t *restrict p, const uint8_t * restrict end)
+{
+    assert(p < end);
+
+    end-=2;
+    p++;
+    for(;p<end; p+=2){
+        if(!*p){
+            if     (!p[-1] && p[1]) return p - 1;
+            else if(!p[ 1] && p[2]) return p;
+        }
+    }
+    return end+2;
+}
+
 /**
  * decodes the group of blocks / video packet header.
  * @return bit position of the resync_marker, or <0 if none was found

libavcodec/mpegvideo.h

@@ -836,6 +836,7 @@ void ff_clean_h263_qscales(MpegEncContext *s);
 int ff_mpeg4_decode_partitions(MpegEncContext *s);
 int ff_mpeg4_get_video_packet_prefix_length(MpegEncContext *s);
 int ff_h263_resync(MpegEncContext *s);
+const uint8_t *ff_h263_find_resync_marker(const uint8_t *p, const uint8_t *end);
 int ff_h263_get_gob_height(MpegEncContext *s);
 void ff_mpeg4_init_direct_mv(MpegEncContext *s);
 int ff_mpeg4_set_direct_mv(MpegEncContext *s, int mx, int my);