CEA608: Fix repeated Special North American chars.

We currently handle most the control code logic after handling special
characters. This includes filtering out repeated control codes and checking
for the correct channel. As the special character sets are control codes as well,
these checks should happen before parsing the characters.

Issue:#6133
PiperOrigin-RevId: 256993672

RELEASENOTES.md

@@ -25,6 +25,8 @@
 * SmoothStreaming: Parse text stream `Subtype` into `Format.roleFlags`.
 * FLV: Fix bug that caused playback of some live streams to not start
   ([#6111](https://github.com/google/ExoPlayer/issues/6111)).
+* CEA608: Fix repetition of special North American characters
+  ([#6133](https://github.com/google/ExoPlayer/issues/6133)).
 
 ### 2.10.2 ###
 

library/core/src/main/java/com/google/android/exoplayer2/text/cea/Cea608Decoder.java

@@ -242,7 +242,7 @@ public final class Cea608Decoder extends CeaDecoder {
   private int captionMode;
   private int captionRowCount;
 
-  private boolean captionValid;
+  private boolean isCaptionValid;
   private boolean repeatableControlSet;
   private byte repeatableControlCc1;
   private byte repeatableControlCc2;
@@ -300,7 +300,7 @@ public final class Cea608Decoder extends CeaDecoder {
     setCaptionMode(CC_MODE_UNKNOWN);
     setCaptionRowCount(DEFAULT_CAPTIONS_ROW_COUNT);
     resetCueBuilders();
-    captionValid = false;
+    isCaptionValid = false;
     repeatableControlSet = false;
     repeatableControlCc1 = 0;
     repeatableControlCc2 = 0;
@@ -358,13 +358,19 @@ public final class Cea608Decoder extends CeaDecoder {
         continue;
       }
 
-      boolean repeatedControlPossible = repeatableControlSet;
-      repeatableControlSet = false;
+      boolean previousIsCaptionValid = isCaptionValid;
+      isCaptionValid =
+          (ccHeader & CC_VALID_FLAG) == CC_VALID_FLAG
+              && ODD_PARITY_BYTE_TABLE[ccByte1]
+              && ODD_PARITY_BYTE_TABLE[ccByte2];
+
+      if (isRepeatedCommand(isCaptionValid, ccData1, ccData2)) {
+        // Ignore repeated valid commands.
+        continue;
+      }
 
-      boolean previousCaptionValid = captionValid;
-      captionValid = (ccHeader & CC_VALID_FLAG) == CC_VALID_FLAG;
-      if (!captionValid) {
-        if (previousCaptionValid) {
+      if (!isCaptionValid) {
+        if (previousIsCaptionValid) {
           // The encoder has flipped the validity bit to indicate captions are being turned off.
           resetCueBuilders();
           captionDataProcessed = true;
@@ -372,15 +378,6 @@ public final class Cea608Decoder extends CeaDecoder {
         continue;
       }
 
-      // If we've reached this point then there is data to process; flag that work has been done.
-      captionDataProcessed = true;
-
-      if (!ODD_PARITY_BYTE_TABLE[ccByte1] || !ODD_PARITY_BYTE_TABLE[ccByte2]) {
-        // The data is invalid.
-        resetCueBuilders();
-        continue;
-      }
-
       maybeUpdateIsInCaptionService(ccData1, ccData2);
       if (!isInCaptionService) {
         // Only the Captioning service is supported. Drop all other bytes.
@@ -393,26 +390,29 @@ public final class Cea608Decoder extends CeaDecoder {
       }
 
       if (isCtrlCode(ccData1)) {
-        if (isSpecialChar(ccData1, ccData2)) {
-          // Special North American character.
-          currentCueBuilder.append(getSpecialChar(ccData2));
+        if (isSpecialNorthAmericanChar(ccData1, ccData2)) {
+          currentCueBuilder.append(getSpecialNorthAmericanChar(ccData2));
         } else if (isExtendedWestEuropeanChar(ccData1, ccData2)) {
-          // Extended West European character.
           // Remove standard equivalent of the special extended char before appending new one.
           currentCueBuilder.backspace();
           currentCueBuilder.append(getExtendedWestEuropeanChar(ccData1, ccData2));
-        } else {
-          // Non-character control code.
-          handleCtrl(ccData1, ccData2, repeatedControlPossible);
+        } else if (isMidrowCtrlCode(ccData1, ccData2)) {
+          handleMidrowCtrl(ccData2);
+        } else if (isPreambleAddressCode(ccData1, ccData2)) {
+          handlePreambleAddressCode(ccData1, ccData2);
+        } else if (isTabCtrlCode(ccData1, ccData2)) {
+          currentCueBuilder.tabOffset = ccData2 - 0x20;
+        } else if (isMiscCode(ccData1, ccData2)) {
+          handleMiscCode(ccData2);
+        }
+      } else {
+        // Basic North American character set.
+        currentCueBuilder.append(getBasicChar(ccData1));
+        if ((ccData2 & 0xE0) != 0x00) {
+          currentCueBuilder.append(getBasicChar(ccData2));
         }
-        continue;
-      }
-
-      // Basic North American character set.
-      currentCueBuilder.append(getChar(ccData1));
-      if ((ccData2 & 0xE0) != 0x00) {
-        currentCueBuilder.append(getChar(ccData2));
       }
+      captionDataProcessed = true;
     }
 
     if (captionDataProcessed) {
@@ -429,14 +429,15 @@ public final class Cea608Decoder extends CeaDecoder {
     return currentChannel == selectedChannel;
   }
 
-  private void handleCtrl(byte cc1, byte cc2, boolean repeatedControlPossible) {
+  private boolean isRepeatedCommand(boolean captionValid, byte cc1, byte cc2) {
     // Most control commands are sent twice in succession to ensure they are received properly. We
     // don't want to process duplicate commands, so if we see the same repeatable command twice in a
     // row then we ignore the second one.
-    if (isRepeatable(cc1)) {
-      if (repeatedControlPossible && repeatableControlCc1 == cc1 && repeatableControlCc2 == cc2) {
+    if (captionValid && isRepeatable(cc1)) {
+      if (repeatableControlSet && repeatableControlCc1 == cc1 && repeatableControlCc2 == cc2) {
         // This is a repeated command, so we ignore it.
-        return;
+        repeatableControlSet = false;
+        return true;
       } else {
         // This is the first occurrence of a repeatable command. Set the repeatable control
         // variables so that we can recognize and ignore a duplicate (if there is one), and then
@@ -445,17 +446,11 @@ public final class Cea608Decoder extends CeaDecoder {
         repeatableControlCc1 = cc1;
         repeatableControlCc2 = cc2;
       }
+    } else {
+      // This command is not repeatable.
+      repeatableControlSet = false;
     }
-
-    if (isMidrowCtrlCode(cc1, cc2)) {
-      handleMidrowCtrl(cc2);
-    } else if (isPreambleAddressCode(cc1, cc2)) {
-      handlePreambleAddressCode(cc1, cc2);
-    } else if (isTabCtrlCode(cc1, cc2)) {
-      currentCueBuilder.tabOffset = cc2 - 0x20;
-    } else if (isMiscCode(cc1, cc2)) {
-      handleMiscCode(cc2);
-    }
+    return false;
   }
 
   private void handleMidrowCtrl(byte cc2) {
@@ -660,18 +655,18 @@ public final class Cea608Decoder extends CeaDecoder {
     }
   }
 
-  private static char getChar(byte ccData) {
+  private static char getBasicChar(byte ccData) {
     int index = (ccData & 0x7F) - 0x20;
     return (char) BASIC_CHARACTER_SET[index];
   }
 
-  private static boolean isSpecialChar(byte cc1, byte cc2) {
+  private static boolean isSpecialNorthAmericanChar(byte cc1, byte cc2) {
     // cc1 - 0|0|0|1|C|0|0|1
     // cc2 - 0|0|1|1|X|X|X|X
     return ((cc1 & 0xF7) == 0x11) && ((cc2 & 0xF0) == 0x30);
   }
 
-  private static char getSpecialChar(byte ccData) {
+  private static char getSpecialNorthAmericanChar(byte ccData) {
     int index = ccData & 0x0F;
     return (char) SPECIAL_CHARACTER_SET[index];
   }