avcodec/mpegutils: Remap MB_TYPE_ACPRED, add codec-specific MB_TYPE

MB_TYPE_ACPRED is currently reused for MB_TYPE_REF0 by H.264,
so that the value fits into an uint16_t. Given that MB_TYPE_ACPRED
is not subject to any such restriction (apart from fitting into
32bits), it can be remapped to a hithereto unused bit.
The then available bit will be declared to be codec-specific
(i.e. unused by generic code), so that H.264 can use it
for MB_TYPE_REF0 and so that it can be reused later for
e.g. MB_TYPE_H261_FIL.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

libavcodec/h264_parse.h

@@ -33,7 +33,7 @@
 #include "get_bits.h"
 #include "h264_ps.h"
 
-#define MB_TYPE_REF0       MB_TYPE_ACPRED // dirty but it fits in 16 bit
+#define MB_TYPE_REF0       MB_TYPE_CODEC_SPECIFIC
 #define MB_TYPE_8x8DCT     0x01000000
 
 // This table must be here because scan8[constant] must be known at compiletime

libavcodec/mpegutils.c

@@ -109,7 +109,7 @@ static char get_type_mv_char(int mb_type)
     // Type & MV direction
     if (IS_PCM(mb_type))
         return 'P';
-    else if (IS_INTRA(mb_type) && IS_ACPRED(mb_type))
+    else if (IS_ACPRED(mb_type))
         return 'A';
     else if (IS_INTRA4x4(mb_type))
         return 'i';

libavcodec/mpegutils.h

@@ -45,7 +45,6 @@
 #define MB_TYPE_8x8        (1 <<  6)
 #define MB_TYPE_INTERLACED (1 <<  7)
 #define MB_TYPE_DIRECT2    (1 <<  8) // FIXME
-#define MB_TYPE_ACPRED     (1 <<  9)
 #define MB_TYPE_GMC        (1 << 10)
 #define MB_TYPE_SKIP       (1 << 11)
 #define MB_TYPE_P0L0       (1 << 12)
@@ -57,9 +56,13 @@
 #define MB_TYPE_L0L1       (MB_TYPE_L0   | MB_TYPE_L1)
 #define MB_TYPE_QUANT      (1 << 16)
 #define MB_TYPE_CBP        (1 << 17)
+#define MB_TYPE_ACPRED     (1 << 18)
 
 #define MB_TYPE_INTRA    MB_TYPE_INTRA4x4 // default mb_type if there is just one type
 
+// The following MB-type can be used by each codec as it sees fit.
+#define MB_TYPE_CODEC_SPECIFIC  (1 << 9)
+
 #define IS_INTRA4x4(a)   ((a) & MB_TYPE_INTRA4x4)
 #define IS_INTRA16x16(a) ((a) & MB_TYPE_INTRA16x16)
 #define IS_PCM(a)        ((a) & MB_TYPE_INTRA_PCM)