dirac_parser: Improve parsing and silence pointless warnings

The parser scans for "BBCD" to appear in the bitstream which indicate a
parse info header and once that happens, checks if the parse offsets are
sane. Since random BBCD strings might appear in the bitstream the parser
will emit a pointless warning if that happens.

This commit improves parsing by checking for a valid parse code as well
as keeping the original checks for valid parse offsets. The warnings
were removed as they serve no real purpose.
Signed-off-by: Rostislav Pehlivanov <atomnuker@gmail.com>

libavcodec/dirac_parser.c

@@ -100,7 +100,11 @@ typedef struct DiracParseUnit {
 static int unpack_parse_unit(DiracParseUnit *pu, DiracParseContext *pc,
                              int offset)
 {
+    int i;
     int8_t *start;
+    static const uint8_t valid_pu_types[] = {
+        0x00, 0x10, 0x20, 0x30, 0x08, 0x48, 0xC8, 0xE8
+    };
 
     if (offset < 0 || pc->index - 13 < offset)
         return 0;
@@ -111,17 +115,20 @@ static int unpack_parse_unit(DiracParseUnit *pu, DiracParseContext *pc,
     pu->next_pu_offset = AV_RB32(start + 5);
     pu->prev_pu_offset = AV_RB32(start + 9);
 
+    /* Check for valid parse code */
+    for (i = 0; i < 8; i++)
+        if (valid_pu_types[i] == pu->pu_type)
+            break;
+    if (i == 8)
+        return 0;
+
     if (pu->pu_type == 0x10 && pu->next_pu_offset == 0)
-        pu->next_pu_offset = 13;
+        pu->next_pu_offset = 13; /* The length of a parse info header */
 
-    if (pu->next_pu_offset && pu->next_pu_offset < 13) {
-        av_log(NULL, AV_LOG_ERROR, "next_pu_offset %d is invalid\n", pu->next_pu_offset);
+    /* Check if the parse offsets are somewhat sane */
+    if ((pu->next_pu_offset && pu->next_pu_offset < 13) ||
+        (pu->prev_pu_offset && pu->prev_pu_offset < 13))
         return 0;
-    }
-    if (pu->prev_pu_offset && pu->prev_pu_offset < 13) {
-        av_log(NULL, AV_LOG_ERROR, "prev_pu_offset %d is invalid\n", pu->prev_pu_offset);
-        return 0;
-    }
 
     return 1;
 }