feat(CEA): Support alignment in CEA-608 (#7022)

Closes #2940

Author: avelad

lib/cea/cea608_data_channel.js

@@ -123,19 +123,26 @@ shaka.cea.Cea608DataChannel = class {
   controlPac_(b1, b2) {
     const row = this.pacToRow_(b1, b2);
 
-    // Get attribute bits (4 bits)
-    const attr = (b2 & 0x1E) >> 1;
-
     // Set up the defaults.
     let textColor = shaka.cea.CeaUtils.DEFAULT_TXT_COLOR;
     let italics = false;
+    let indent = null;
+
+    // Get PAC index;
+    let pacIndex;
+    if (b2 > 0x5f) {
+      pacIndex = b2 - 0x60;
+    } else {
+      pacIndex = b2 - 0x40;
+    }
 
-
-    // Attributes < 7 are colors, = 7 is white w/ italics, and >7 are indents
-    if (attr < 7) {
-      textColor = shaka.cea.Cea608DataChannel.TEXT_COLORS[attr];
-    } else if (attr === 7) {
+    if (pacIndex <= 0xd) {
+      const colorIndex = Math.floor(pacIndex / 2);
+      textColor = shaka.cea.Cea608DataChannel.TEXT_COLORS[colorIndex];
+    } else if (pacIndex <= 0xf) {
       italics = true; // color stays white
+    } else {
+      indent = Math.floor((pacIndex - 0x10) / 2);
     }
 
     // PACs toggle underline on the last bit of b2.
@@ -168,6 +175,7 @@ shaka.cea.Cea608DataChannel = class {
     buf.setUnderline(underline);
     buf.setItalics(italics);
     buf.setTextColor(textColor);
+    buf.setIndent(indent);
 
     // Clear the background color, since new row (PAC) should reset ALL styles.
     buf.setBackgroundColor(shaka.cea.CeaUtils.DEFAULT_BG_COLOR);
@@ -507,6 +515,16 @@ shaka.cea.Cea608DataChannel = class {
     this.curbuf_.addChar(charSet, b2);
   }
 
+  /**
+   * Handles a tab offset.
+   *
+   * @param {number} offset
+   * @private
+   */
+  handleOffset_(offset) {
+    this.curbuf_.setOffset(offset);
+  }
+
   /**
    * Decodes control code.
    * Three types of control codes:
@@ -543,6 +561,9 @@ shaka.cea.Cea608DataChannel = class {
       this.handleExtendedWesternEuropeanChar_(b1, b2);
     } else if (this.isMiscellaneous_(b1, b2)) {
       return this.controlMiscellaneous_(ccPacket);
+    } else if (this.isOffset_(b1, b2)) {
+      const offset = b2 - 0x20;
+      this.handleOffset_(offset);
     }
     return null;
   }
@@ -561,6 +582,17 @@ shaka.cea.Cea608DataChannel = class {
     return ((b1 & 0xf6) === 0x14) && ((b2 & 0xf0) === 0x20);
   }
 
+  /**
+   * Checks if this is a offset control code.
+   * @param {number} b1 Byte 1.
+   * @param {number} b2 Byte 2.
+   * @return {boolean}
+   * @private
+   */
+  isOffset_(b1, b2) {
+    return (b1 == 0x17 || b1 == 0x1f) && b2 >= 0x21 && b2 <= 0x23;
+  }
+
   /**
    * Checks if this is a PAC control code.
    * @param {number} b1 Byte 1.

lib/cea/cea608_memory.js

@@ -69,6 +69,16 @@ shaka.cea.Cea608Memory = class {
      */
     this.backgroundColor_ = shaka.cea.CeaUtils.DEFAULT_BG_COLOR;
 
+    /**
+     * @private {?number}
+     */
+    this.offset_ = null;
+
+    /**
+     * @private {?number}
+     */
+    this.indent_ = null;
+
     this.reset();
   }
 
@@ -89,6 +99,10 @@ shaka.cea.Cea608Memory = class {
     if (line) {
       topLevelCue.line = line;
     }
+    if (this.indent_ != null && this.offset_ != null) {
+      topLevelCue.position = 10 + Math.min(70, this.indent_ * 10) +
+          this.offset_ * 2.5;
+    }
     const ret = shaka.cea.CeaUtils.getParsedCaption(
         topLevelCue, stream, this.rows_, startTime, endTime);
     // If the text and its lines are larger than what we can show on the
@@ -270,6 +284,20 @@ shaka.cea.Cea608Memory = class {
   setBackgroundColor(color) {
     this.backgroundColor_ = color;
   }
+
+  /**
+   * @param {number} offset
+   */
+  setOffset(offset) {
+    this.offset_ = offset;
+  }
+
+  /**
+   * @param {?number} indent
+   */
+  setIndent(indent) {
+    this.indent_ = indent;
+  }
 };
 
 /**