Add font-size support to WebVTT CssParser.

This CL addresses the github issue [#8946](https://github.com/google/ExoPlayer/issues/8964). That issue requests support for `font-size` CSS property in WebVTT subtitle format. This CL:
* Adds support for `font-size` property by extending capabilities of WebVTT `CssParser`. Implementation of `font-size` property value parsing is based on the one in `TtmlDecoder`.
* Adds unit test along with test file containing WebVTT subtitles with all currently supported `font-size` units.

#minor-release

PiperOrigin-RevId: 388423859

RELEASENOTES.md

@@ -117,6 +117,8 @@
 *   Text:
     *   TTML: Inherit the `rubyPosition` value from a containing `<span
         ruby="container">` element.
+    *   WebVTT: Add support for CSS `font-size` property
+        ([#8964](https://github.com/google/ExoPlayer/issues/8964)).
 *   Ad playback:
     *   Support changing ad break positions in the player logic
         ([#5067](https://github.com/google/ExoPlayer/issues/5067).

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

@@ -20,8 +20,10 @@ import androidx.annotation.Nullable;
 import com.google.android.exoplayer2.text.span.TextAnnotation;
 import com.google.android.exoplayer2.util.Assertions;
 import com.google.android.exoplayer2.util.ColorParser;
+import com.google.android.exoplayer2.util.Log;
 import com.google.android.exoplayer2.util.ParsableByteArray;
 import com.google.android.exoplayer2.util.Util;
+import com.google.common.base.Ascii;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.regex.Matcher;
@@ -31,9 +33,9 @@ import java.util.regex.Pattern;
  * Provides a CSS parser for STYLE blocks in Webvtt files. Supports only a subset of the CSS
  * features.
  */
-/* package */ final class CssParser {
+/* package */ final class WebvttCssParser {
 
-  private static final String TAG = "CssParser";
+  private static final String TAG = "WebvttCssParser";
 
   private static final String RULE_START = "{";
   private static final String RULE_END = "}";
@@ -41,6 +43,7 @@ import java.util.regex.Pattern;
   private static final String PROPERTY_BGCOLOR = "background-color";
   private static final String PROPERTY_FONT_FAMILY = "font-family";
   private static final String PROPERTY_FONT_WEIGHT = "font-weight";
+  private static final String PROPERTY_FONT_SIZE = "font-size";
   private static final String PROPERTY_RUBY_POSITION = "ruby-position";
   private static final String VALUE_OVER = "over";
   private static final String VALUE_UNDER = "under";
@@ -54,12 +57,14 @@ import java.util.regex.Pattern;
   private static final String VALUE_ITALIC = "italic";
 
   private static final Pattern VOICE_NAME_PATTERN = Pattern.compile("\\[voice=\"([^\"]*)\"\\]");
+  private static final Pattern FONT_SIZE_PATTERN =
+      Pattern.compile("^((?:[0-9]*\\.)?[0-9]+)(px|em|%)$");
 
   // Temporary utility data structures.
   private final ParsableByteArray styleInput;
   private final StringBuilder stringBuilder;
 
-  public CssParser() {
+  public WebvttCssParser() {
     styleInput = new ParsableByteArray();
     stringBuilder = new StringBuilder();
   }
@@ -213,6 +218,8 @@ import java.util.regex.Pattern;
       if (VALUE_ITALIC.equals(value)) {
         style.setItalic(true);
       }
+    } else if (PROPERTY_FONT_SIZE.equals(property)) {
+      parseFontSize(value, style);
     }
     // TODO: Fill remaining supported styles.
   }
@@ -336,6 +343,31 @@ import java.util.regex.Pattern;
     return stringBuilder.toString();
   }
 
+  private static void parseFontSize(String fontSize, WebvttCssStyle style) {
+    Matcher matcher = FONT_SIZE_PATTERN.matcher(Ascii.toLowerCase(fontSize));
+    if (!matcher.matches()) {
+      Log.w(TAG, "Invalid font-size: '" + fontSize + "'.");
+      return;
+    }
+    String unit = Assertions.checkNotNull(matcher.group(2));
+    switch (unit) {
+      case "px":
+        style.setFontSizeUnit(WebvttCssStyle.FONT_SIZE_UNIT_PIXEL);
+        break;
+      case "em":
+        style.setFontSizeUnit(WebvttCssStyle.FONT_SIZE_UNIT_EM);
+        break;
+      case "%":
+        style.setFontSizeUnit(WebvttCssStyle.FONT_SIZE_UNIT_PERCENT);
+        break;
+      default:
+        // this line should never be reached because when the fontSize matches the FONT_SIZE_PATTERN
+        // unit must be one of: px, em, %
+        throw new IllegalStateException();
+    }
+    style.setFontSize(Float.parseFloat(Assertions.checkNotNull(matcher.group(1))));
+  }
+
   /**
    * Sets the target of a {@link WebvttCssStyle} by splitting a selector of the form {@code
    * ::cue(tag#id.class1.class2[voice="someone"]}, where every element is optional.

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

@@ -263,7 +263,7 @@ public final class WebvttCssStyle {
     return this;
   }
 
-  public WebvttCssStyle setFontSizeUnit(short unit) {
+  public WebvttCssStyle setFontSizeUnit(@FontSizeUnit int unit) {
     this.fontSizeUnit = unit;
     return this;
   }

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

@@ -44,12 +44,12 @@ public final class WebvttDecoder extends SimpleSubtitleDecoder {
   private static final String STYLE_START = "STYLE";
 
   private final ParsableByteArray parsableWebvttData;
-  private final CssParser cssParser;
+  private final WebvttCssParser cssParser;
 
   public WebvttDecoder() {
     super("WebvttDecoder");
     parsableWebvttData = new ParsableByteArray();
-    cssParser = new CssParser();
+    cssParser = new WebvttCssParser();
   }
 
   @Override

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

@@ -15,7 +15,7 @@
  */
 package com.google.android.exoplayer2.text.webvtt;
 
-import static com.google.android.exoplayer2.text.webvtt.CssParser.parseNextToken;
+import static com.google.android.exoplayer2.text.webvtt.WebvttCssParser.parseNextToken;
 import static com.google.common.truth.Truth.assertThat;
 
 import androidx.test.ext.junit.runners.AndroidJUnit4;
@@ -29,15 +29,15 @@ import org.junit.Before;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 
-/** Unit test for {@link CssParser}. */
+/** Unit test for {@link WebvttCssParser}. */
 @RunWith(AndroidJUnit4.class)
-public final class CssParserTest {
+public final class WebvttCssParserTest {
 
-  private CssParser parser;
+  private WebvttCssParser parser;
 
   @Before
   public void setUp() {
-    parser = new CssParser();
+    parser = new WebvttCssParser();
   }
 
   @Test
@@ -232,13 +232,13 @@ public final class CssParserTest {
 
   private void assertSkipsToEndOfSkip(String expectedLine, String s) {
     ParsableByteArray input = new ParsableByteArray(Util.getUtf8Bytes(s));
-    CssParser.skipWhitespaceAndComments(input);
+    WebvttCssParser.skipWhitespaceAndComments(input);
     assertThat(input.readLine()).isEqualTo(expectedLine);
   }
 
   private void assertInputLimit(String expectedLine, String s) {
     ParsableByteArray input = new ParsableByteArray(Util.getUtf8Bytes(s));
-    CssParser.skipStyleBlock(input);
+    WebvttCssParser.skipStyleBlock(input);
     assertThat(input.readLine()).isEqualTo(expectedLine);
   }
 

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

@@ -54,6 +54,7 @@ public class WebvttDecoderTest {
   private static final String WITH_BAD_CUE_HEADER_FILE = "media/webvtt/with_bad_cue_header";
   private static final String WITH_TAGS_FILE = "media/webvtt/with_tags";
   private static final String WITH_CSS_STYLES = "media/webvtt/with_css_styles";
+  private static final String WITH_FONT_SIZE = "media/webvtt/with_font_size";
   private static final String WITH_CSS_COMPLEX_SELECTORS =
       "media/webvtt/with_css_complex_selectors";
   private static final String WITH_CSS_TEXT_COMBINE_UPRIGHT =
@@ -400,6 +401,58 @@ public class WebvttDecoderTest {
     assertThat(secondCue.text.toString()).isEqualTo("This is the third subtitle.");
   }
 
+  @Test
+  public void decodeWithCssFontSizeStyle() throws Exception {
+    WebvttSubtitle subtitle = getSubtitleForTestAsset(WITH_FONT_SIZE);
+
+    assertThat(subtitle.getEventTimeCount()).isEqualTo(12);
+
+    assertThat(subtitle.getEventTime(0)).isEqualTo(0L);
+    assertThat(subtitle.getEventTime(1)).isEqualTo(2_000_000L);
+    Cue firstCue = Iterables.getOnlyElement(subtitle.getCues(subtitle.getEventTime(0)));
+    assertThat(firstCue.text.toString()).isEqualTo("Sentence with font-size set to 4.4em.");
+    assertThat((Spanned) firstCue.text)
+        .hasRelativeSizeSpanBetween(0, "Sentence with font-size set to 4.4em.".length())
+        .withSizeChange(4.4f);
+
+    assertThat(subtitle.getEventTime(2)).isEqualTo(2_100_000L);
+    assertThat(subtitle.getEventTime(3)).isEqualTo(2_400_000L);
+    Cue secondCue = Iterables.getOnlyElement(subtitle.getCues(subtitle.getEventTime(2)));
+    assertThat(secondCue.text.toString()).isEqualTo("Sentence with bad font-size unit.");
+    assertThat((Spanned) secondCue.text).hasNoSpans();
+
+    assertThat(subtitle.getEventTime(4)).isEqualTo(2_500_000L);
+    assertThat(subtitle.getEventTime(5)).isEqualTo(4_000_000L);
+    Cue thirdCue = Iterables.getOnlyElement(subtitle.getCues(subtitle.getEventTime(4)));
+    assertThat(thirdCue.text.toString()).isEqualTo("Absolute font-size expressed in px unit!");
+    assertThat((Spanned) thirdCue.text)
+        .hasAbsoluteSizeSpanBetween(0, "Absolute font-size expressed in px unit!".length())
+        .withAbsoluteSize(2);
+
+    assertThat(subtitle.getEventTime(6)).isEqualTo(4_500_000L);
+    assertThat(subtitle.getEventTime(7)).isEqualTo(6_000_000L);
+    Cue fourthCue = Iterables.getOnlyElement(subtitle.getCues(subtitle.getEventTime(6)));
+    assertThat(fourthCue.text.toString()).isEqualTo("Relative font-size expressed in % unit!");
+    assertThat((Spanned) fourthCue.text)
+        .hasRelativeSizeSpanBetween(0, "Relative font-size expressed in % unit!".length())
+        .withSizeChange(0.035f);
+
+    assertThat(subtitle.getEventTime(8)).isEqualTo(6_100_000L);
+    assertThat(subtitle.getEventTime(9)).isEqualTo(6_400_000L);
+    Cue fifthCue = Iterables.getOnlyElement(subtitle.getCues(subtitle.getEventTime(8)));
+    assertThat(fifthCue.text.toString()).isEqualTo("Sentence with bad font-size value.");
+    assertThat((Spanned) secondCue.text).hasNoSpans();
+
+    assertThat(subtitle.getEventTime(10)).isEqualTo(6_500_000L);
+    assertThat(subtitle.getEventTime(11)).isEqualTo(8_000_000L);
+    Cue sixthCue = Iterables.getOnlyElement(subtitle.getCues(subtitle.getEventTime(10)));
+    assertThat(sixthCue.text.toString())
+        .isEqualTo("Upper and lower case letters in font-size unit.");
+    assertThat((Spanned) sixthCue.text)
+        .hasAbsoluteSizeSpanBetween(0, "Upper and lower case letters in font-size unit.".length())
+        .withAbsoluteSize(2);
+  }
+
   @Test
   public void webvttWithCssStyle() throws Exception {
     WebvttSubtitle subtitle = getSubtitleForTestAsset(WITH_CSS_STYLES);

testdata/src/test/assets/media/webvtt/with_font_size

@@ -0,0 +1,49 @@
+WEBVTT
+
+STYLE
+::cue(.unit-em) {
+  font-size: 4.4em;
+}
+
+STYLE
+::cue(.unit-px) {
+  font-size: 2px;
+}
+
+STYLE
+::cue(.unit-percent) {
+  font-size: 3.5%
+}
+
+STYLE
+::cue(.case-insensitivity) {
+  font-size: 2Px;
+}
+
+STYLE
+::cue(.bad-unit) {
+  font-size: 4.4ef;
+}
+
+STYLE
+::cue(.bad-value) {
+  font-size: 3.5.5%
+}
+
+00:00.000 --> 00:02.000
+<c.unit-em>Sentence with font-size set to 4.4em.</c>
+
+00:02.100 --> 00:02.400
+<c.bad-unit>Sentence with bad font-size unit.</c>
+
+00:02.500 --> 00:04.000
+<c.unit-px>Absolute font-size expressed in px unit!</c>
+
+00:04.500 --> 00:06.000
+<c.unit-percent>Relative font-size expressed in % unit!</c>
+
+00:06.100 --> 00:06.400
+<c.bad-value>Sentence with bad font-size value.</c>
+
+00:06.500 --> 00:08.000
+<c.case-insensitivity>Upper and lower case letters in font-size unit.</c>