h264: Add stream constraint values to the common header

With comments describing the derivation of each value.

libavcodec/h264.h

@@ -44,4 +44,49 @@ enum {
     H264_NAL_AUXILIARY_SLICE = 19,
 };
 
+
+enum {
+    // 7.4.2.1.1: seq_parameter_set_id is in [0, 31].
+    H264_MAX_SPS_COUNT = 32,
+    // 7.4.2.2: pic_parameter_set_id is in [0, 255].
+    H264_MAX_PPS_COUNT = 256,
+
+    // A.3: MaxDpbFrames is bounded above by 16.
+    H264_MAX_DPB_FRAMES = 16,
+    // 7.4.2.1.1: max_num_ref_frames is in [0, MaxDpbFrames], and
+    // each reference frame can have two fields.
+    H264_MAX_REFS       = 2 * H264_MAX_DPB_FRAMES,
+
+    // 7.4.3.1: modification_of_pic_nums_idc is not equal to 3 at most
+    // num_ref_idx_lN_active_minus1 + 1 times (that is, once for each
+    // possible reference), then equal to 3 once.
+    H264_MAX_RPLM_COUNT = H264_MAX_REFS + 1,
+
+    // 7.4.3.3: in the worst case, we begin with a full short-term
+    // reference picture list.  Each picture in turn is moved to the
+    // long-term list (type 3) and then discarded from there (type 2).
+    // Then, we set the length of the long-term list (type 4), mark
+    // the current picture as long-term (type 6) and terminate the
+    // process (type 0).
+    H264_MAX_MMCO_COUNT = H264_MAX_REFS * 2 + 3,
+
+    // A.2.1, A.2.3: profiles supporting FMO constrain
+    // num_slice_groups_minus1 to be in [0, 7].
+    H264_MAX_SLICE_GROUPS = 8,
+
+    // E.2.2: cpb_cnt_minus1 is in [0, 31].
+    H264_MAX_CPB_CNT = 32,
+
+    // A.3: in table A-1 the highest level allows a MaxFS of 139264.
+    H264_MAX_MB_PIC_SIZE = 139264,
+    // A.3.1, A.3.2: PicWidthInMbs and PicHeightInMbs are constrained
+    // to be not greater than sqrt(MaxFS * 8).  Hence height/width are
+    // bounded above by sqrt(139264 * 8) = 1055.5 macroblocks.
+    H264_MAX_MB_WIDTH    = 1055,
+    H264_MAX_MB_HEIGHT   = 1055,
+    H264_MAX_WIDTH       = H264_MAX_MB_WIDTH  * 16,
+    H264_MAX_HEIGHT      = H264_MAX_MB_HEIGHT * 16,
+};
+
+
 #endif /* AVCODEC_H264_H */