feat: Add SubStation Alpha (SSA) support (#3060)

Format info: https://en.wikipedia.org/wiki/SubStation_Alpha
shaka-project · Feb 1, 2021 · 0845843 · 0845843
1 parent 54b8f6e
commit 0845843
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Showing 9 changed files with 835 additions and 35 deletions.
diff --git a/README.md b/README.md
@@ -211,6 +211,8 @@ Shaka Player supports:
     - UTF-8 encoding only
   - LyRiCs (LRC)
     - UTF-8 encoding only
+  - SubStation Alpha (SSA, ASS)
+    - UTF-8 encoding only
 
 Subtitles are rendered by the browser by default.  Applications can create a
 [text display plugin][] for customer rendering to go beyond browser-supported

diff --git a/build/types/text b/build/types/text
@@ -4,5 +4,7 @@
 +../../lib/text/mp4_ttml_parser.js
 +../../lib/text/mp4_vtt_parser.js
 +../../lib/text/srt_text_parser.js
++../../lib/text/ssa_text_parser.js
 +../../lib/text/ttml_text_parser.js
 +../../lib/text/vtt_text_parser.js
++../../lib/text/web_vtt_generator.js
diff --git a/lib/player.js b/lib/player.js
@@ -33,6 +33,7 @@ goog.require('shaka.routing.Walker');
 goog.require('shaka.text.SimpleTextDisplayer');
 goog.require('shaka.text.TextEngine');
 goog.require('shaka.text.UITextDisplayer');
+goog.require('shaka.text.WebVttGenerator');
 goog.require('shaka.util.AbortableOperation');
 goog.require('shaka.util.ConfigUtils');
 goog.require('shaka.util.Error');
@@ -3913,6 +3914,8 @@ shaka.Player = class extends shaka.util.FakeEventTarget {
         'webvtt': 'text/vtt',
         'ttml': 'application/ttml+xml',
         'lrc': 'application/x-subtitle-lrc',
+        'ssa': 'text/x-ssa',
+        'ass': 'text/x-ssa',
       }[extension];
 
       if (!mimeType) {
@@ -4058,6 +4061,8 @@ shaka.Player = class extends shaka.util.FakeEventTarget {
         'webvtt': 'text/vtt',
         'ttml': 'application/ttml+xml',
         'lrc': 'application/x-subtitle-lrc',
+        'ssa': 'text/x-ssa',
+        'ass': 'text/x-ssa',
       }[extension];
 
       if (!mimeType) {
@@ -4234,10 +4239,12 @@ shaka.Player = class extends shaka.util.FakeEventTarget {
             mimeType);
       }
     }
+    /** @type {Array.<!shaka.extern.Cue>} */
+    let cues;
     if (mimeType === 'application/x-subtitle-lrc') {
       const LrcTextParser = shaka.text.LrcTextParser;
       if (LrcTextParser) {
-        return LrcTextParser.convertToWebVTT(data, this.video_.duration);
+        cues = LrcTextParser.getCues(data, this.video_.duration);
       } else {
         throw new shaka.util.Error(
             shaka.util.Error.Severity.CRITICAL,
@@ -4246,6 +4253,21 @@ shaka.Player = class extends shaka.util.FakeEventTarget {
             mimeType);
       }
     }
+    if (mimeType === 'text/x-ssa') {
+      const SsaTextParser = shaka.text.SsaTextParser;
+      if (SsaTextParser) {
+        cues = SsaTextParser.getCues(data);
+      } else {
+        throw new shaka.util.Error(
+            shaka.util.Error.Severity.CRITICAL,
+            shaka.util.Error.Category.TEXT,
+            shaka.util.Error.Code.MISSING_TEXT_PLUGIN,
+            mimeType);
+      }
+    }
+    if (cues) {
+      return shaka.text.WebVttGenerator.convert(cues);
+    }
     throw new shaka.util.Error(
         shaka.util.Error.Severity.RECOVERABLE,
         shaka.util.Error.Category.TEXT,

diff --git a/lib/text/lrc_text_parser.js b/lib/text/lrc_text_parser.js
@@ -33,16 +33,15 @@ shaka.text.LrcTextParser = class {
    * @export
    */
   parseMedia(data, time) {
-    return shaka.text.LrcTextParser.getCues_(data, time.segmentEnd);
+    return shaka.text.LrcTextParser.getCues(data, time.segmentEnd);
   }
 
   /**
    * @param {BufferSource} data
    * @param {number} segmentEnd
    * @return {!Array.<!shaka.extern.Cue>}
-   * @private
    */
-  static getCues_(data, segmentEnd) {
+  static getCues(data, segmentEnd) {
     const StringUtils = shaka.util.StringUtils;
     const LrcTextParser = shaka.text.LrcTextParser;
 
@@ -101,37 +100,6 @@ shaka.text.LrcTextParser = class {
     const seconds = parseFloat(match[2].replace(',', '.'));
     return minutes * 60 + seconds;
   }
-
-  /**
-   * Convert a LRC input to WebVTT
-   *
-   * @param {BufferSource} data
-   * @param {number} segmentEnd
-   * @return {string}
-   * @export
-   */
-  static convertToWebVTT(data, segmentEnd) {
-    const LrcTextParser = shaka.text.LrcTextParser;
-    const cues = LrcTextParser.getCues_(data, segmentEnd);
-    let webvttString = 'WEBVTT\n\n';
-    for (const cue of cues) {
-      const webvttTimeString = (time) => {
-        const hours = Math.floor(time / 3600);
-        const minutes = Math.floor(time / 60 % 60);
-        const seconds = Math.floor(time % 60);
-        const milliseconds = Math.floor(time * 1000 % 1000);
-        return (hours < 10 ? '0' : '') + hours + ':' +
-            (minutes < 10 ? '0' : '') + minutes + ':' +
-            (seconds < 10 ? '0' : '') + seconds + '.' +
-            (milliseconds < 100 ? (milliseconds < 10 ? '00' : '0') : '') +
-            milliseconds;
-      };
-      webvttString += webvttTimeString(cue.startTime) + ' --> ' +
-          webvttTimeString(cue.endTime) + '\n';
-      webvttString += cue.payload + '\n\n';
-    }
-    return webvttString;
-  }
 };
 
 /**