mpegts: Define the section length with a constant

The specification says the value is expressed in 10 bits including
the 4-byte CRC.

libavformat/mpegtsenc.c

@@ -89,6 +89,10 @@ typedef struct MpegTSWrite {
 #define DEFAULT_PES_HEADER_FREQ 16
 #define DEFAULT_PES_PAYLOAD_SIZE ((DEFAULT_PES_HEADER_FREQ - 1) * 184 + 170)
 
+/* The section length is 12 bits. The first 2 are set to 0, the remaining
+ * 10 bits should not exceed 1021. */
+#define SECTION_LENGTH 1020
+
 /* NOTE: 4 bytes must be left at the end for the crc32 */
 static void mpegts_write_section(MpegTSSection *s, uint8_t *buf, int len)
 {
@@ -201,7 +205,7 @@ static void mpegts_write_pat(AVFormatContext *s)
 {
     MpegTSWrite *ts = s->priv_data;
     MpegTSService *service;
-    uint8_t data[1012], *q;
+    uint8_t data[SECTION_LENGTH], *q;
     int i;
 
     q = data;
@@ -217,7 +221,7 @@ static void mpegts_write_pat(AVFormatContext *s)
 static void mpegts_write_pmt(AVFormatContext *s, MpegTSService *service)
 {
     MpegTSWrite *ts = s->priv_data;
-    uint8_t data[1012], *q, *desc_length_ptr, *program_info_length_ptr;
+    uint8_t data[SECTION_LENGTH], *q, *desc_length_ptr, *program_info_length_ptr;
     int val, stream_type, i;
 
     q = data;
@@ -372,7 +376,7 @@ static void mpegts_write_sdt(AVFormatContext *s)
 {
     MpegTSWrite *ts = s->priv_data;
     MpegTSService *service;
-    uint8_t data[1012], *q, *desc_list_len_ptr, *desc_len_ptr;
+    uint8_t data[SECTION_LENGTH], *q, *desc_list_len_ptr, *desc_len_ptr;
     int i, running_status, free_ca_mode, val;
 
     q = data;