Assign class 2 to most macroblocks by default, instead of a more conservative

method defined by SMPTE

Patch by Dan Maas

Originally committed as revision 5074 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/dv.c

@@ -658,8 +658,22 @@ static always_inline void dv_set_class_number(DCTELEM* blk, EncBlockInfo* bi,
                                               const uint8_t* zigzag_scan, const int *weight, int bias)
 {
     int i, area;
+    /* We offer two different methods for class number assignment: the
+       method suggested in SMPTE 314M Table 22, and an improved
+       method. The SMPTE method is very conservative; it assigns class
+       3 (i.e. severe quantization) to any block where the largest AC
+       component is greater than 36. ffmpeg's DV encoder tracks AC bit
+       consumption precisely, so there is no need to bias most blocks
+       towards strongly lossy compression. Instead, we assign class 2
+       to most blocks, and use class 3 only when strictly necessary
+       (for blocks whose largest AC component exceeds 255). */
+
+#if 0 /* SMPTE spec method */
     static const int classes[] = {12, 24, 36, 0xffff};
-    int max=12;
+#else /* improved ffmpeg method */
+    static const int classes[] = {-1, -1, 255, 0xffff};
+#endif
+    int max=classes[0];
     int prev=0;
 
     bi->mb[0] = blk[0];

tests/ffmpeg.regression.ref

@@ -133,10 +133,10 @@ stddev: 23.20 PSNR:20.81 bytes:7602176
 3533710 ./data/a-snow53.avi
 799d3db687f6cdd7a837ec156efc171f *./data/out.yuv
 stddev:  0.00 PSNR:99.99 bytes:7602176
-1352049a75c5c94f21a360888b12d75d *./data/a-dv.dv
+85529d9838c5a8aef041445fa8ef3c85 *./data/a-dv.dv
 7200000 ./data/a-dv.dv
-2c7f745a74c1ac25566b6c49ed619649 *./data/out.yuv
-stddev:  9.00 PSNR:29.03 bytes:7602176
+c2082cd8adf417c4ebc32654e446cba1 *./data/out.yuv
+stddev:  8.86 PSNR:29.17 bytes:7602176
 bd0db310a36ad94bcd4448abe0a88368 *./data/a-svq1.mov
 1379827 ./data/a-svq1.mov
 bbff871d1475e1eee4231a08e075de2c *./data/out.yuv

tests/libav.regression.ref

@@ -28,9 +28,9 @@ e4ed8d635d867e2f5980fd9c73c9cf3d *./data/b-libav.mov
 8bf16d40a2ec19fa36b124a928e47e23 *./data/b-libav.nut
  332358 ./data/b-libav.nut
 ./data/b-libav.nut CRC=0xccab3a27
-afe55c5769eb6d1873d4106b3ef2b691 *./data/b-libav.dv
+2cc647904d3cca01703f36056b9d3f42 *./data/b-libav.dv
 3600000 ./data/b-libav.dv
-./data/b-libav.dv CRC=0x9292dedd
+./data/b-libav.dv CRC=0xa6b8b635
 9a9da315747599f7718cc9a9a09c21ff *./data/b-libav.pbm
  317075 ./data/b-libav.pbm
 ./data/b-libav.pbm CRC=0xb92906cb

tests/rotozoom.regression.ref

@@ -133,10 +133,10 @@ stddev: 10.94 PSNR:27.34 bytes:7602176
 2725570 ./data/a-snow53.avi
 dde5895817ad9d219f79a52d0bdfb001 *./data/out.yuv
 stddev:  0.00 PSNR:99.99 bytes:7602176
-3d7def2ed47e896790945c3c634fa4e8 *./data/a-dv.dv
+6568326ee439099e8a0e1680336ed351 *./data/a-dv.dv
 7200000 ./data/a-dv.dv
-49020c3651d58137db4dc56ca13ff26d *./data/out.yuv
-stddev:  3.06 PSNR:38.40 bytes:7602176
+bb69dda7a84a5b166434e28e1243d3d1 *./data/out.yuv
+stddev:  2.99 PSNR:38.59 bytes:7602176
 5b02b6ae7ffa257a66ae9857a992fdfe *./data/a-svq1.mov
 769527 ./data/a-svq1.mov
 44777d1ddbccd0ef7f8d08394465670c *./data/out.yuv