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CEA608: Fix repeated Special North American chars.
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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
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@tonihei @ojw28
tonihei authored and ojw28 committed Jul 8, 2019
1 parent ecd88c7 commit e3af045
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Showing 2 changed files with 45 additions and 48 deletions.
2 changes: 2 additions & 0 deletions RELEASENOTES.md
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Original file line number Diff line number Diff line change
Expand Up @@ -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 ###

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91 changes: 43 additions & 48 deletions library/core/src/main/java/com/google/android/exoplayer2/text/cea/Cea608Decoder.java
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Original file line number Diff line number Diff line change
Expand Up @@ -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;
Expand Down Expand Up @@ -300,7 +300,7 @@ public void flush() {
setCaptionMode(CC_MODE_UNKNOWN);
setCaptionRowCount(DEFAULT_CAPTIONS_ROW_COUNT);
resetCueBuilders();
captionValid = false;
isCaptionValid = false;
repeatableControlSet = false;
repeatableControlCc1 = 0;
repeatableControlCc2 = 0;
Expand Down Expand Up @@ -358,29 +358,26 @@ protected void decode(SubtitleInputBuffer inputBuffer) {
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;
}
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.
Expand All @@ -393,26 +390,29 @@ protected void decode(SubtitleInputBuffer inputBuffer) {
}

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) {
Expand All @@ -429,14 +429,15 @@ private boolean updateAndVerifyCurrentChannel(byte cc1) {
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
Expand All @@ -445,17 +446,11 @@ private void handleCtrl(byte cc1, byte cc2, boolean repeatedControlPossible) {
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) {
Expand Down Expand Up @@ -660,18 +655,18 @@ private void maybeUpdateIsInCaptionService(byte cc1, byte cc2) {
}
}

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];
}
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