Skip SSA cues where end time is before or equal to start time

The file in Issue: androidx/media#2052 contains a cue with the following timecode:

```
0:00:00:00,0:00:00:00
```

The content of this cue seems to be some 'converted by' metadata, i.e.
it's basically a comment and clearly not intended to be shown on
screen (since it has zero duration).

There is some fiddly logic later in `SsaParser` to support overlapping
cues with the old `Subtitle` structure [1], and this logic gets tripped
up by the start and end time being equal, which results in a
**single**, empty `List<Cue>` being added - which trips up another
assumption that every SSA cue line results in at least two `List<Cue>`
entries (one containing the cue text, and another containing an empty
list to signal the end of the cues).

This fiddly logic is no longer required, because overlapping
`CuesWithTiming` objects can now be merged in `TextRenderer`, so there
is a possible future simplification to `SsaParser` which removes a lot
of this complexity.

[1] Added in <unknown commit>

PiperOrigin-RevId: 718380386

RELEASENOTES.md

@@ -63,6 +63,9 @@
         ([#8260](https://github.com/google/ExoPlayer/issues/8260)).
     *   Fix playback hanging when a playlist contains clipped items with CEA-608
         or CEA-708 captions.
+    *   Fix `IllegalStateException` when an SSA file contains a cue with zero
+        duration (start and end time equal)
+        ([#2052](https://github.com/androidx/media/issues/2052)).
 *   Metadata:
 *   Image:
 *   DataSource:

libraries/exoplayer/src/test/java/androidx/media3/exoplayer/text/DelegatingSubtitleDecoderWithSsaParserTest.java

@@ -342,16 +342,23 @@ public final class DelegatingSubtitleDecoderWithSsaParserTest {
     assertThat(firstCue.line).isEqualTo(Cue.DIMEN_UNSET);
   }
 
+  /**
+   * Parsing should succeed, skipping the cues with invalid time codes, and parsing the third and
+   * final cues only.
+   */
   @Test
   public void decodeInvalidTimecodes() throws IOException {
-    // Parsing should succeed, parsing the third cue only.
     DelegatingSubtitleDecoder decoder = new DelegatingSubtitleDecoder("SSA", new SsaParser());
     byte[] bytes =
         TestUtil.getByteArray(ApplicationProvider.getApplicationContext(), INVALID_TIMECODES);
     Subtitle subtitle = decoder.decode(bytes, bytes.length, false);
 
-    assertThat(subtitle.getEventTimeCount()).isEqualTo(2);
+    assertThat(subtitle.getEventTimeCount()).isEqualTo(4);
     assertTypicalCue3(subtitle, 0);
+    assertThat(subtitle.getEventTime(2)).isEqualTo(16_560_000);
+    assertThat(subtitle.getEventTime(3)).isEqualTo(17_900_000);
+    assertThat(Iterables.getOnlyElement(subtitle.getCues(16_560_000)).text.toString())
+        .isEqualTo("This is the last subtitle.");
   }
 
   @Test

libraries/extractor/src/main/java/androidx/media3/extractor/text/ssa/SsaParser.java

@@ -334,7 +334,7 @@ public final class SsaParser implements SubtitleParser {
     }
 
     long endTimeUs = parseTimecodeUs(lineValues[format.endTimeIndex]);
-    if (endTimeUs == C.TIME_UNSET) {
+    if (endTimeUs == C.TIME_UNSET || endTimeUs <= startTimeUs) {
       Log.w(TAG, "Skipping invalid timing: " + dialogueLine);
       return;
     }

libraries/extractor/src/test/java/androidx/media3/extractor/text/ssa/SsaParserTest.java

@@ -425,16 +425,25 @@ public final class SsaParserTest {
     assertThat(firstCue.line).isEqualTo(Cue.DIMEN_UNSET);
   }
 
+  /**
+   * Parsing should succeed, skipping the cues with invalid time codes, and parsing the third and
+   * final cues only.
+   */
   @Test
   public void parseInvalidTimecodes() throws IOException {
-    // Parsing should succeed, parsing the third cue only.
     SsaParser parser = new SsaParser();
     byte[] bytes =
         TestUtil.getByteArray(ApplicationProvider.getApplicationContext(), INVALID_TIMECODES);
     ImmutableList<CuesWithTiming> allCues = parseAllCues(parser, bytes);
 
-    assertThat(allCues).hasSize(1);
-    assertTypicalCue3(Iterables.getOnlyElement(allCues));
+    assertThat(allCues).hasSize(2);
+    assertTypicalCue3(allCues.get(0));
+    CuesWithTiming finalCue = allCues.get(1);
+    assertThat(finalCue.startTimeUs).isEqualTo(16_560_000);
+    assertThat(finalCue.endTimeUs).isEqualTo(17_900_000);
+    assertThat(finalCue.durationUs).isEqualTo(1_340_000);
+    assertThat(Iterables.getOnlyElement(finalCue.cues).text.toString())
+        .isEqualTo("This is the last subtitle.");
   }
 
   @Test

libraries/test_data/src/test/assets/media/ssa/invalid_timecodes

@@ -7,8 +7,12 @@ Style: Default,Open Sans Semibold,36,&H00FFFFFF,&H000000FF,&H00020713,&H00000000
 
 [Events]
 Format: Layer, Start, End, Style, Name, Text
-Dialogue: 0,Invalid,0:00:01.23,Default,Olly,This is the first subtitle{ignored}.
-Dialogue: 0,0:00:02.34,Invalid,Default,Olly,This is the second subtitle \nwith a newline \Nand another.
+Dialogue: 0,Invalid,0:00:01.23,Default,Olly,Non-integer start time.
+Dialogue: 0,0:00:02.34,Invalid,Default,Olly,Non-integer end time.
 Dialogue: 0,0:00:04:56,0:00:08:90,Default,Olly,This is the third subtitle, with a comma.
-Dialogue: 0,          ,0:00:10:90,Default,Olly,This is the fourth subtitle.
-Dialogue: 0,0:00:12:90,          ,Default,Olly,This is the fifth subtitle.
+Dialogue: 0,          ,0:00:10:90,Default,Olly,Empty start time.
+Dialogue: 0,0:00:12:90,          ,Default,Olly,Empty end time.
+Dialogue: 0,0:00:13:90,0:00:13:90,Default,Olly,Start and end time equal.
+Dialogue: 0,0:00:15:90,0:00:14:90,Default,Olly,End time before start time.
+Dialogue: 0,0:00:16:56,0:00:17:90,Default,Olly,This is the last subtitle.
+