This pull request is for issue#1807. Refactoring the PR #8356

In this change -

Handling the sequence number discontinuity in caption channel packet header.

The processCurrentPacket returns if the packet length does not match with the currentIndex. That assumption is wrong. As per spec the the packet can end on reception of next cc_type = 0x3.

library/core/src/main/java/com/google/android/exoplayer2/text/cea/Cea708Decoder.java

@@ -145,6 +145,7 @@ public final class Cea708Decoder extends CeaDecoder {
 
   private final ParsableByteArray ccData;
   private final ParsableBitArray serviceBlockPacket;
+  private int lastSequenceNo = -1;
   // TODO: Use isWideAspectRatio in decoding.
   @SuppressWarnings({"unused", "FieldCanBeLocal"})
   private final boolean isWideAspectRatio;
@@ -231,6 +232,13 @@ protected void decode(SubtitleInputBuffer inputBuffer) {
         finalizeCurrentPacket();
 
         int sequenceNumber = (ccData1 & 0xC0) >> 6; // first 2 bits
+        if (lastSequenceNo != -1 && sequenceNumber != (lastSequenceNo + 1) % 4) {
+          resetCueBuilders();
+          Log.w(TAG, "discontinuity in sequence number detected : lastSequenceNo = " +
+              lastSequenceNo + " sequenceNumber = " + sequenceNumber);
+        }
+        lastSequenceNo = sequenceNumber;
+
         int packetSize = ccData1 & 0x3F; // last 6 bits
         if (packetSize == 0) {
           packetSize = 64;
@@ -270,10 +278,11 @@ private void finalizeCurrentPacket() {
   @RequiresNonNull("currentDtvCcPacket")
   private void processCurrentPacket() {
     if (currentDtvCcPacket.currentIndex != (currentDtvCcPacket.packetSize * 2 - 1)) {
-      Log.w(TAG, "DtvCcPacket ended prematurely; size is " + (currentDtvCcPacket.packetSize * 2 - 1)
+      Log.d(TAG, "DtvCcPacket ended prematurely; size is " + (currentDtvCcPacket.packetSize * 2 - 1)
           + ", but current index is " + currentDtvCcPacket.currentIndex + " (sequence number "
-          + currentDtvCcPacket.sequenceNumber + "); ignoring packet");
-      return;
+          + currentDtvCcPacket.sequenceNumber + ");");
+      // This is not invalid packet. As per CEA-708 section 4.4.1.1, the Packect end can happen
+      // when the reception of cc_type = 0x03 (binary 11).
     }
 
     serviceBlockPacket.reset(currentDtvCcPacket.packetData, currentDtvCcPacket.currentIndex);