hevc_nal: add is_hvcC helper

Tries strongest match against decoder record

modules/mux/mp4/libmp4mux.c

@@ -592,7 +592,7 @@ static bo_t *GetHvcCTag(es_format_t *p_fmt)
     size_t i_buffer = p_fmt->i_extra;
 
     /* Extradata is already an HEVCDecoderConfigurationRecord */
-    if(i_buffer > 16 && p_buffer[0] == 0x01)
+    if(hevc_ishvcC(p_buffer, i_buffer))
     {
         (void) bo_add_mem(hvcC, i_buffer, p_buffer);
         return hvcC;

modules/packetizer/hevc_nal.h

@@ -63,6 +63,22 @@ enum hevc_nal_unit_type_e
     HEVC_NAL_UNKNOWN
 };
 
+#define HEVC_MIN_HVCC_SIZE 22
+
+/* checks if data is an HEVCDecoderConfigurationRecord */
+static inline bool hevc_ishvcC( const uint8_t *p_buf, size_t i_buf )
+{
+    return ( i_buf >= HEVC_MIN_HVCC_SIZE &&
+             p_buf[0] == 0x01 &&
+            (p_buf[13] & 0xF0) == 0xF0 && /* Match all reserved bits */
+            (p_buf[15] & 0xFC) == 0xFC &&
+            (p_buf[16] & 0xFC) == 0xFC &&
+            (p_buf[17] & 0xF8) == 0xF8 &&
+            (p_buf[18] & 0xF8) == 0xF8 &&
+            (p_buf[21] & 0x03) != 0x02
+           );
+}
+
 /* Converts HEVCDecoderConfigurationRecord to Annex B format */
 int hevc_hvcC_to_AnnexB_NAL( decoder_t *p_dec, const uint8_t *p_buf,
                             uint32_t i_buf_size, uint8_t *p_out_buf,