vp3: Skip the loop filter when strength is 0 or when requested

Originally committed as revision 23346 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/vp3.c

@@ -136,6 +136,7 @@ typedef struct Vp3DecodeContext {
     DSPContext dsp;
     int flipped_image;
     int last_slice_end;
+    int skip_loop_filter;
 
     int qps[3];
     int nqps;
@@ -1494,6 +1495,7 @@ static void render_slice(Vp3DecodeContext *s, int slice)
             }
 
             // Filter up to the last row in the superblock row
+            if (!s->skip_loop_filter)
                 apply_loop_filter(s, plane, 4*sb_y - !!sb_y, FFMIN(4*sb_y+3, fragment_height-1));
         }
     }
@@ -1749,6 +1751,9 @@ static int vp3_decode_frame(AVCodecContext *avctx,
             s->keyframe?"key":"", counter, s->qps[0]);
     counter++;
 
+    s->skip_loop_filter = !s->filter_limit_values[s->qps[0]] ||
+        avctx->skip_loop_filter >= (s->keyframe ? AVDISCARD_ALL : AVDISCARD_NONKEY);
+
     if (s->qps[0] != s->last_qps[0])
         init_loop_filter(s);