CEA-608: Only truncate to 32 visible characters

We introduced truncation to 32 chars in <unknown commit>
and included indent and offset in the calculation. I think this is
technically correct, but it causes problems with the content in
Issue: google/ExoPlayer#11019 and it doesn't seem a problem to only truncate actual
cue text (i.e. ignore offset and indent).

PiperOrigin-RevId: 544677965
(cherry picked from commit e8fdd83)

RELEASENOTES.md

@@ -5,6 +5,11 @@
 *   ExoPlayer:
     *   Fix issue in `PlaybackStatsListener` where spurious `PlaybackStats` are
         created after the playlist is cleared.
+*   Text:
+    *   CEA-608: Change cue truncation logic to only consider visible text.
+        Previously indent and tab offset were included when limiting the cue
+        length to 32 characters (which was technically correct by the spec)
+        ([#11019](https://github.com/google/ExoPlayer/issues/11019)).
 ## 1.1
 
 ### 1.1.0 (2023-07-05)

libraries/common/src/main/java/androidx/media3/common/util/Util.java

@@ -1675,25 +1675,6 @@ public static long toLong(int mostSignificantBits, int leastSignificantBits) {
     return (toUnsignedLong(mostSignificantBits) << 32) | toUnsignedLong(leastSignificantBits);
   }
 
-  /**
-   * Truncates a sequence of ASCII characters to a maximum length.
-   *
-   * <p>This preserves span styling in the {@link CharSequence}. If that's not important, use {@link
-   * Ascii#truncate(CharSequence, int, String)}.
-   *
-   * <p><b>Note:</b> This is not safe to use in general on Unicode text because it may separate
-   * characters from combining characters or split up surrogate pairs.
-   *
-   * @param sequence The character sequence to truncate.
-   * @param maxLength The max length to truncate to.
-   * @return {@code sequence} directly if {@code sequence.length() <= maxLength}, otherwise {@code
-   *     sequence.subsequence(0, maxLength}.
-   */
-  @UnstableApi
-  public static CharSequence truncateAscii(CharSequence sequence, int maxLength) {
-    return sequence.length() <= maxLength ? sequence : sequence.subSequence(0, maxLength);
-  }
-
   /**
    * Returns a byte array containing values parsed from the hex string provided.
    *

libraries/common/src/test/java/androidx/media3/common/util/UtilTest.java

@@ -38,10 +38,6 @@
 import android.os.Handler;
 import android.os.HandlerThread;
 import android.os.Looper;
-import android.text.SpannableString;
-import android.text.Spanned;
-import android.text.style.StrikethroughSpan;
-import android.text.style.UnderlineSpan;
 import android.util.SparseLongArray;
 import androidx.media3.common.C;
 import androidx.media3.test.utils.TestUtil;
@@ -896,45 +892,6 @@ public void toLong_withBigNegativeValue_returnsValue() {
     assertThat(Util.toLong(0xFEDCBA, 0x87654321)).isEqualTo(0xFEDCBA_87654321L);
   }
 
-  @Test
-  public void truncateAscii_shortInput_returnsInput() {
-    String input = "a short string";
-
-    assertThat(Util.truncateAscii(input, 100)).isSameInstanceAs(input);
-  }
-
-  @Test
-  public void truncateAscii_longInput_truncated() {
-    String input = "a much longer string";
-
-    assertThat(Util.truncateAscii(input, 5).toString()).isEqualTo("a muc");
-  }
-
-  @Test
-  public void truncateAscii_preservesStylingSpans() {
-    SpannableString input = new SpannableString("a short string");
-    input.setSpan(new UnderlineSpan(), 0, 10, Spanned.SPAN_EXCLUSIVE_EXCLUSIVE);
-    input.setSpan(new StrikethroughSpan(), 4, 10, Spanned.SPAN_INCLUSIVE_EXCLUSIVE);
-
-    CharSequence result = Util.truncateAscii(input, 7);
-
-    assertThat(result).isInstanceOf(SpannableString.class);
-    assertThat(result.toString()).isEqualTo("a short");
-    // TODO(internal b/161804035): Use SpannedSubject when it's available in a dependency we can use
-    // from here.
-    Spanned spannedResult = (Spanned) result;
-    Object[] spans = spannedResult.getSpans(0, result.length(), Object.class);
-    assertThat(spans).hasLength(2);
-    assertThat(spans[0]).isInstanceOf(UnderlineSpan.class);
-    assertThat(spannedResult.getSpanStart(spans[0])).isEqualTo(0);
-    assertThat(spannedResult.getSpanEnd(spans[0])).isEqualTo(7);
-    assertThat(spannedResult.getSpanFlags(spans[0])).isEqualTo(Spanned.SPAN_EXCLUSIVE_EXCLUSIVE);
-    assertThat(spans[1]).isInstanceOf(StrikethroughSpan.class);
-    assertThat(spannedResult.getSpanStart(spans[1])).isEqualTo(4);
-    assertThat(spannedResult.getSpanEnd(spans[1])).isEqualTo(7);
-    assertThat(spannedResult.getSpanFlags(spans[1])).isEqualTo(Spanned.SPAN_INCLUSIVE_EXCLUSIVE);
-  }
-
   @Test
   public void toHexString_returnsHexString() {
     byte[] bytes = createByteArray(0x12, 0xFC, 0x06);

libraries/extractor/src/main/java/androidx/media3/extractor/text/cea/Cea608Decoder.java

@@ -35,7 +35,6 @@
 import androidx.media3.common.util.Log;
 import androidx.media3.common.util.ParsableByteArray;
 import androidx.media3.common.util.UnstableApi;
-import androidx.media3.common.util.Util;
 import androidx.media3.extractor.text.Subtitle;
 import androidx.media3.extractor.text.SubtitleDecoder;
 import androidx.media3.extractor.text.SubtitleDecoderException;
@@ -949,8 +948,7 @@ public void backspace() {
     }
 
     public void append(char text) {
-      // Don't accept more than 32 chars. We'll trim further, considering indent & tabOffset, in
-      // build().
+      // Don't accept more than 32 chars.
       if (captionStringBuilder.length() < SCREEN_CHARWIDTH) {
         captionStringBuilder.append(text);
       }
@@ -968,24 +966,23 @@ public void rollUp() {
 
     @Nullable
     public Cue build(@Cue.AnchorType int forcedPositionAnchor) {
-      // The number of empty columns before the start of the text, in the range [0-31].
-      int startPadding = indent + tabOffset;
-      int maxTextLength = SCREEN_CHARWIDTH - startPadding;
       SpannableStringBuilder cueString = new SpannableStringBuilder();
       // Add any rolled up captions, separated by new lines.
       for (int i = 0; i < rolledUpCaptions.size(); i++) {
-        cueString.append(Util.truncateAscii(rolledUpCaptions.get(i), maxTextLength));
+        cueString.append(rolledUpCaptions.get(i));
         cueString.append('\n');
       }
       // Add the current line.
-      cueString.append(Util.truncateAscii(buildCurrentLine(), maxTextLength));
+      cueString.append(buildCurrentLine());
 
       if (cueString.length() == 0) {
         // The cue is empty.
         return null;
       }
 
       int positionAnchor;
+      // The number of empty columns before the start of the text, in the range [0-31].
+      int startPadding = indent + tabOffset;
       // The number of empty columns after the end of the text, in the same range.
       int endPadding = SCREEN_CHARWIDTH - startPadding - cueString.length();
       int startEndPaddingDelta = startPadding - endPadding;