Update WebVttCueParser to parse position alignment values

Currently we assume these are "start", "center", "middle" or "end",
which was correct in a previous draft of the spec:
https://www.w3.org/TR/2014/WD-webvtt1-20141111/#dfn-webvtt-text-position-cue-setting

The released spec uses "line-left", "center" and "line-right":
https://www.w3.org/TR/webvtt1/#webvtt-position-cue-setting

PiperOrigin-RevId: 307371066

RELEASENOTES.md

@@ -89,6 +89,12 @@
         [issue #6581](https://github.com/google/ExoPlayer/issues/6581)).
     *   Parse `tts:ruby` and `tts:rubyPosition` properties in TTML subtitles
         (rendering is coming later).
+    *   Update WebVTT position alignment parsing to recognise `line-left`,
+        `center` and `line-right` as per the
+        [released spec](https://www.w3.org/TR/webvtt1/#webvtt-position-cue-setting)
+        (a
+        [previous draft](https://www.w3.org/TR/2014/WD-webvtt1-20141111/#dfn-webvtt-text-position-cue-setting)
+        used `start`, `middle` and `end`).
 *   DRM:
     *   Add support for attaching DRM sessions to clear content in the demo app.
     *   Remove `DrmSessionManager` references from all renderers.

library/core/src/main/java/com/google/android/exoplayer2/text/webvtt/WebvttCueParser.java

@@ -387,7 +387,7 @@ public final class WebvttCueParser {
   private static void parseLineAttribute(String s, WebvttCueInfoBuilder builder) {
     int commaIndex = s.indexOf(',');
     if (commaIndex != -1) {
-      builder.lineAnchor = parsePositionAnchor(s.substring(commaIndex + 1));
+      builder.lineAnchor = parseLineAnchor(s.substring(commaIndex + 1));
       s = s.substring(0, commaIndex);
     }
     if (s.endsWith("%")) {
@@ -405,6 +405,22 @@ public final class WebvttCueParser {
     }
   }
 
+  @Cue.AnchorType
+  private static int parseLineAnchor(String s) {
+    switch (s) {
+      case "start":
+        return Cue.ANCHOR_TYPE_START;
+      case "center":
+      case "middle":
+        return Cue.ANCHOR_TYPE_MIDDLE;
+      case "end":
+        return Cue.ANCHOR_TYPE_END;
+      default:
+        Log.w(TAG, "Invalid anchor value: " + s);
+        return Cue.TYPE_UNSET;
+    }
+  }
+
   private static void parsePositionAttribute(String s, WebvttCueInfoBuilder builder) {
     int commaIndex = s.indexOf(',');
     if (commaIndex != -1) {
@@ -417,11 +433,13 @@ public final class WebvttCueParser {
   @Cue.AnchorType
   private static int parsePositionAnchor(String s) {
     switch (s) {
+      case "line-left":
       case "start":
         return Cue.ANCHOR_TYPE_START;
       case "center":
       case "middle":
         return Cue.ANCHOR_TYPE_MIDDLE;
+      case "line-right":
       case "end":
         return Cue.ANCHOR_TYPE_END;
       default:

library/core/src/test/java/com/google/android/exoplayer2/text/webvtt/WebvttDecoderTest.java

@@ -184,14 +184,14 @@ public class WebvttDecoderTest {
   public void decodeWithPositioning() throws Exception {
     WebvttSubtitle subtitle = getSubtitleForTestAsset(WITH_POSITIONING_FILE);
 
-    assertThat(subtitle.getEventTimeCount()).isEqualTo(12);
+    assertThat(subtitle.getEventTimeCount()).isEqualTo(16);
 
     assertThat(subtitle.getEventTime(0)).isEqualTo(0L);
     assertThat(subtitle.getEventTime(1)).isEqualTo(1_234_000L);
     Cue firstCue = Iterables.getOnlyElement(subtitle.getCues(subtitle.getEventTime(0)));
     assertThat(firstCue.text.toString()).isEqualTo("This is the first subtitle.");
-    assertThat(firstCue.position).isEqualTo(0.1f);
-    assertThat(firstCue.positionAnchor).isEqualTo(Cue.ANCHOR_TYPE_START);
+    assertThat(firstCue.position).isEqualTo(0.6f);
+    assertThat(firstCue.positionAnchor).isEqualTo(Cue.ANCHOR_TYPE_END);
     assertThat(firstCue.textAlignment).isEqualTo(Alignment.ALIGN_NORMAL);
     assertThat(firstCue.size).isEqualTo(0.35f);
     // Unspecified values should use WebVTT defaults
@@ -246,6 +246,18 @@ public class WebvttDecoderTest {
     // Derived from `align:center`:
     assertThat(sixthCue.position).isEqualTo(0.5f);
     assertThat(sixthCue.positionAnchor).isEqualTo(Cue.ANCHOR_TYPE_MIDDLE);
+
+    assertThat(subtitle.getEventTime(12)).isEqualTo(12_000_000L);
+    assertThat(subtitle.getEventTime(13)).isEqualTo(13_000_000L);
+    Cue seventhCue = Iterables.getOnlyElement(subtitle.getCues(subtitle.getEventTime(12)));
+    assertThat(seventhCue.text.toString()).isEqualTo("This is the seventh subtitle.");
+    assertThat(seventhCue.positionAnchor).isEqualTo(Cue.ANCHOR_TYPE_START);
+
+    assertThat(subtitle.getEventTime(14)).isEqualTo(14_000_000L);
+    assertThat(subtitle.getEventTime(15)).isEqualTo(15_000_000L);
+    Cue eighthCue = Iterables.getOnlyElement(subtitle.getCues(subtitle.getEventTime(14)));
+    assertThat(eighthCue.text.toString()).isEqualTo("This is the eighth subtitle.");
+    assertThat(eighthCue.positionAnchor).isEqualTo(Cue.ANCHOR_TYPE_END);
   }
 
   @Test

testdata/src/test/assets/webvtt/with_positioning

@@ -2,7 +2,7 @@ WEBVTT
 
 NOTE Position with percentage and position alignment
 
-00:00:00.000 --> 00:00:01.234 position:10%,start align:start size:35%
+00:00:00.000 --> 00:00:01.234 position:60%,end align:start size:35%
 This is the first subtitle.
 
 NOTE Wrong position provided. It should be provided as
@@ -30,3 +30,13 @@ NOTE In newer drafts, align:middle has been replaced by align:center
 
 00:10.000 --> 00:11.000 align:center
 This is the sixth subtitle.
+
+NOTE In older drafts position alignment could be start,middle,end
+
+00:12.000 --> 00:13.000 position:20%,start
+This is the seventh subtitle.
+
+NOTE In the released spec position alignment can be line-left,center,line-right
+
+00:14.000 --> 00:15.000 position:70%,line-right
+This is the eighth subtitle.