[ogg-dev] [PATCH] liboggz: Fix Dirac bitstream parsing

[Ralph Giles]

On Tue, Nov 4, 2008 at 12:56 AM, David Flynn <davidf+nntp at woaf.net> wrote:

> Quite a while ago, the specification was modified to change the
> way the nondefault scan format was signalled; this patch fixes that.

Thanks for the patch. I've tried to fix things as discussed on irc.
Please review r3762.

Index: /liboggz/trunk/src/liboggz/dirac.c
===================================================================
--- /liboggz/trunk/src/liboggz/dirac.c (revision 3665)
+++ /liboggz/trunk/src/liboggz/dirac.c (revision 3762)
@@ -116,9 +116,16 @@
     {1,1}, /* this first value is never used */
     {24000,1001}, {24,1}, {25,1}, {30000,1001}, {30,1},
-    {50,1}, {60000,1001}, {60,1}, {15000,1001}, {25,2},
+    {50,1}, {60000,1001}, {60,1}, {15000,1001}, {25,2}
   };

   static const ogg_uint32_t dirac_vidfmt_frate[] = { /* table C.1 */
-    1, 9, 10, 9, 10, 9, 10, 4, 3, 7, 6, 4, 3, 7, 6, 2, 2, 7, 6, 7, 6,
+    1, 9, 10, 9, 10, 9, 10, 4, 3, 7, 6, 4, 3, 7, 6, 2, 2, 7, 6, 7, 6
+  };
+
+  static const int dirac_source_sampling[] = { /* extracted from table C.1 */
+    0, 0, 0, 0, 0, 0, 0, 1, 1, 0, 0, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0
+  };
+  static const int dirac_top_field_first[] = { /* from table C.1 */
+    0, 0, 1, 0, 1, 0, 1, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1
   };

@@ -151,11 +158,17 @@
     info->chroma_format = dirac_uint( &bs ); /* chroma_format */
   }
-  if (dirac_bool( &bs )) {
-    info->interlaced = 0;
-    if (dirac_bool( &bs )) { /* interlaced */
-        info->interlaced = 1;
-        info->top_field_first = dirac_bool( &bs ); /* top_field_first */
+
+  if (dirac_bool( &bs )) { /* custom_scan_format_flag */
+    int scan_format = dirac_uint( &bs ); /* scan_format */
+    if (scan_format < 2) {
+      info->interlaced = scan_format;
+    } else { /* other scan_format values are reserved */
+      info->interlaced = 0;
     }
+  } else { /* no custom scan_format, use the preset value */
+    info->interlaced = dirac_source_sampling[video_format];
   }
+  /* field order is set by video_format and cannot be custom */
+  info->top_field_first = dirac_top_field_first[video_format];

   info->fps_numerator =
dirac_frate_tbl[dirac_vidfmt_frate[video_format]].fps_numerator;