mpegts: Fix for continuity counter

Make continuity counter respect discontinuity flag
and null packets. Unpack the adaptation_field_control field.
Signed-off-by: Zohar Kelrich <lumimies@gmail.com>
Signed-off-by: Luca Barbato <lu_zero@gentoo.org>

libavformat/mpegts.c

@@ -1248,7 +1248,8 @@ static int handle_packet(MpegTSContext *ts, const uint8_t *packet)
 {
     AVFormatContext *s = ts->stream;
     MpegTSFilter *tss;
-    int len, pid, cc, expected_cc, cc_ok, afc, is_start;
+    int len, pid, cc, expected_cc, cc_ok, afc, is_start, is_discontinuity,
+        has_adaptation, has_payload;
     const uint8_t *p, *p_end;
     int64_t pos;
 
@@ -1264,20 +1265,29 @@ static int handle_packet(MpegTSContext *ts, const uint8_t *packet)
     if (!tss)
         return 0;
 
+    afc = (packet[3] >> 4) & 3;
+    if (afc == 0) /* reserved value */
+        return 0;
+    has_adaptation = afc & 2;
+    has_payload = afc & 1;
+    is_discontinuity = has_adaptation
+                && packet[4] != 0 /* with length > 0 */
+                && (packet[5] & 0x80); /* and discontinuity indicated */
+
     /* continuity check (currently not used) */
     cc = (packet[3] & 0xf);
-    expected_cc = (packet[3] & 0x10) ? (tss->last_cc + 1) & 0x0f : tss->last_cc;
-    cc_ok = (tss->last_cc < 0) || (expected_cc == cc);
+    expected_cc = has_payload ? (tss->last_cc + 1) & 0x0f : tss->last_cc;
+    cc_ok = pid == 0x1FFF // null packet PID
+            || is_discontinuity
+            || tss->last_cc < 0
+            || expected_cc == cc;
+
     tss->last_cc = cc;
 
-    /* skip adaptation field */
-    afc = (packet[3] >> 4) & 3;
-    p = packet + 4;
-    if (afc == 0) /* reserved value */
+    if (!has_payload)
         return 0;
-    if (afc == 2) /* adaptation field only */
-        return 0;
-    if (afc == 3) {
+    p = packet + 4;
+    if (has_adaptation) {
         /* skip adapation field */
         p += p[0] + 1;
     }