Skip negative SubRip timecodes

Issue: #2145

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=140868079

library/src/androidTest/assets/subrip/typical_negative_timestamps

@@ -0,0 +1,12 @@
+1
+-0:00:04,567 --> -0:00:03,456
+This is the first subtitle.
+
+2
+-00:00:02,345 --> 00:00:01,234
+This is the second subtitle.
+Second subtitle with second line.
+
+3
+00:00:04,567 --> 00:00:08,901
+This is the third subtitle.

library/src/androidTest/java/com/google/android/exoplayer2/text/subrip/SubripDecoderTest.java

@@ -30,6 +30,7 @@ public final class SubripDecoderTest extends InstrumentationTestCase {
   private static final String TYPICAL_EXTRA_BLANK_LINE = "subrip/typical_extra_blank_line";
   private static final String TYPICAL_MISSING_TIMECODE = "subrip/typical_missing_timecode";
   private static final String TYPICAL_MISSING_SEQUENCE = "subrip/typical_missing_sequence";
+  private static final String TYPICAL_NEGATIVE_TIMESTAMPS = "subrip/typical_negative_timestamps";
   private static final String NO_END_TIMECODES_FILE = "subrip/no_end_timecodes";
 
   public void testDecodeEmpty() throws IOException {
@@ -91,6 +92,15 @@ public final class SubripDecoderTest extends InstrumentationTestCase {
     assertTypicalCue3(subtitle, 2);
   }
 
+  public void testDecodeTypicalNegativeTimestamps() throws IOException {
+    // Parsing should succeed, parsing the third cue only.
+    SubripDecoder decoder = new SubripDecoder();
+    byte[] bytes = TestUtil.getByteArray(getInstrumentation(), TYPICAL_NEGATIVE_TIMESTAMPS);
+    SubripSubtitle subtitle = decoder.decode(bytes, bytes.length);
+    assertEquals(2, subtitle.getEventTimeCount());
+    assertTypicalCue3(subtitle, 0);
+  }
+
   public void testDecodeNoEndTimecodes() throws IOException {
     SubripDecoder decoder = new SubripDecoder();
     byte[] bytes = TestUtil.getByteArray(getInstrumentation(), NO_END_TIMECODES_FILE);

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

@@ -548,7 +548,7 @@ public final class Cea608Decoder extends CeaDecoder {
   private static boolean isPreambleAddressCode(byte cc1, byte cc2) {
     // cc1 - 0|0|0|1|C|X|X|X
     // cc2 - 0|1|X|X|X|X|X|X
-    return ((cc1 & 0xF0) == 0x10) && ((cc2 & 0xC0) == 0x80);
+    return ((cc1 & 0xF0) == 0x10) && ((cc2 & 0xC0) == 0x40);
   }
 
   private static boolean isTabCtrlCode(byte cc1, byte cc2) {

library/src/main/java/com/google/android/exoplayer2/text/subrip/SubripDecoder.java

@@ -34,9 +34,9 @@ public final class SubripDecoder extends SimpleSubtitleDecoder {
 
   private static final String TAG = "SubripDecoder";
 
-  private static final Pattern SUBRIP_TIMING_LINE = Pattern.compile("(\\S*)\\s*-->\\s*(\\S*)");
+  private static final String SUBRIP_TIMECODE = "(?:(\\d+):)?(\\d+):(\\d+),(\\d+)";
-  private static final Pattern SUBRIP_TIMESTAMP =
+  private static final Pattern SUBRIP_TIMING_LINE =
-      Pattern.compile("(?:(\\d+):)?(\\d+):(\\d+),(\\d+)");
+      Pattern.compile("\\s*(" + SUBRIP_TIMECODE + ")\\s*-->\\s*(" + SUBRIP_TIMECODE + ")?\\s*");
 
   private final StringBuilder textBuilder;
 
@@ -50,7 +50,6 @@ public final class SubripDecoder extends SimpleSubtitleDecoder {
     ArrayList<Cue> cues = new ArrayList<>();
     LongArray cueTimesUs = new LongArray();
     ParsableByteArray subripData = new ParsableByteArray(bytes, length);
-    boolean haveEndTimecode;
     String currentLine;
 
     while ((currentLine = subripData.readLine()) != null) {
@@ -68,15 +67,14 @@ public final class SubripDecoder extends SimpleSubtitleDecoder {
       }
 
       // Read and parse the timing line.
-      haveEndTimecode = false;
+      boolean haveEndTimecode = false;
       currentLine = subripData.readLine();
       Matcher matcher = SUBRIP_TIMING_LINE.matcher(currentLine);
-      if (matcher.find()) {
+      if (matcher.matches()) {
-        cueTimesUs.add(parseTimecode(matcher.group(1)));
+        cueTimesUs.add(parseTimecode(matcher, 1));
-        String endTimecode = matcher.group(2);
+        if (!TextUtils.isEmpty(matcher.group(6))) {
-        if (!TextUtils.isEmpty(endTimecode)) {
           haveEndTimecode = true;
-          cueTimesUs.add(parseTimecode(matcher.group(2)));
+          cueTimesUs.add(parseTimecode(matcher, 6));
         }
       } else {
         Log.w(TAG, "Skipping invalid timing: " + currentLine);
@@ -105,15 +103,11 @@ public final class SubripDecoder extends SimpleSubtitleDecoder {
     return new SubripSubtitle(cuesArray, cueTimesUsArray);
   }
 
-  private static long parseTimecode(String s) throws NumberFormatException {
+  private static long parseTimecode(Matcher matcher, int groupOffset) {
-    Matcher matcher = SUBRIP_TIMESTAMP.matcher(s);
+    long timestampMs = Long.parseLong(matcher.group(groupOffset + 1)) * 60 * 60 * 1000;
-    if (!matcher.matches()) {
+    timestampMs += Long.parseLong(matcher.group(groupOffset + 2)) * 60 * 1000;
-      throw new NumberFormatException("has invalid format");
+    timestampMs += Long.parseLong(matcher.group(groupOffset + 3)) * 1000;
-    }
+    timestampMs += Long.parseLong(matcher.group(groupOffset + 4));
-    long timestampMs = Long.parseLong(matcher.group(1)) * 60 * 60 * 1000;
-    timestampMs += Long.parseLong(matcher.group(2)) * 60 * 1000;
-    timestampMs += Long.parseLong(matcher.group(3)) * 1000;
-    timestampMs += Long.parseLong(matcher.group(4));
     return timestampMs * 1000;
   }