mpegts: update comment to match code

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/mpegts.c

@@ -1536,7 +1536,7 @@ static int mpegts_read_header(AVFormatContext *s,
     int len;
     int64_t pos;
 
-    /* read the first 1024 bytes to get packet size */
+    /* read the first 8192 bytes to get packet size */
     pos = avio_tell(pb);
     len = avio_read(pb, buf, sizeof(buf));
     if (len != sizeof(buf))