ssa_text_parser.js

/*! @license
 * Shaka Player
 * Copyright 2016 Google LLC
 * SPDX-License-Identifier: Apache-2.0
 */

goog.provide('shaka.text.SsaTextParser');

goog.require('goog.asserts');
goog.require('shaka.log');
goog.require('shaka.text.Cue');
goog.require('shaka.text.TextEngine');
goog.require('shaka.util.StringUtils');


/**
 * Documentation: http://moodub.free.fr/video/ass-specs.doc
 * https://en.wikipedia.org/wiki/SubStation_Alpha
 * @implements {shaka.extern.TextParser}
 * @export
 */
shaka.text.SsaTextParser = class {
  /**
   * @override
   * @export
   */
  parseInit(data) {
    goog.asserts.assert(false, 'SSA does not have init segments');
  }

  /**
   * @override
   * @export
   */
  setSequenceMode(sequenceMode) {
    // Unused.
  }

  /**
   * @override
   * @export
   */
  parseMedia(data, time) {
    const StringUtils = shaka.util.StringUtils;
    const SsaTextParser = shaka.text.SsaTextParser;

    // Get the input as a string.
    const str = StringUtils.fromUTF8(data);

    const section = {
      styles: '',
      events: '',
    };

    const parts = str.split(/\r?\n\s*\r?\n/);
    for (const part of parts) {
      // SSA content
      const match = SsaTextParser.ssaContent_.exec(part);
      if (match) {
        const tag = match[1];
        const lines = match[2];
        if (tag == 'V4 Styles' || tag == 'V4+ Styles') {
          section.styles = lines;
          continue;
        }
        if (tag == 'Events') {
          section.events = lines;
          continue;
        }
      }
      shaka.log.warning('SsaTextParser parser encountered an unknown part.',
          part);
    }

    // Process styles
    const styles = [];

    // Used to be able to iterate over the style parameters.
    let styleColumns = null;

    const styleLines = section.styles.split(/\r?\n/);
    for (const line of styleLines) {
      if (/^\s*;/.test(line)) {
        // Skip comment
        continue;
      }
      const lineParts = SsaTextParser.lineParts_.exec(line);
      if (lineParts) {
        const name = lineParts[1].trim();
        const value = lineParts[2].trim();
        if (name == 'Format') {
          styleColumns = value.split(SsaTextParser.valuesFormat_);
          continue;
        }
        if (name == 'Style') {
          const values = value.split(SsaTextParser.valuesFormat_);
          const style = {};
          for (let c = 0; c < styleColumns.length && c < values.length; c++) {
            style[styleColumns[c]] = values[c];
          }
          styles.push(style);
          continue;
        }
      }
    }

    // Process cues
    /** @type {!Array.<!shaka.extern.Cue>} */
    const cues = [];

    // Used to be able to iterate over the event parameters.
    let eventColumns = null;

    const eventLines = section.events.split(/\r?\n/);
    for (const line of eventLines) {
      if (/^\s*;/.test(line)) {
        // Skip comment
        continue;
      }
      const lineParts = SsaTextParser.lineParts_.exec(line);
      if (lineParts) {
        const name = lineParts[1].trim();
        const value = lineParts[2].trim();
        if (name == 'Format') {
          eventColumns = value.split(SsaTextParser.valuesFormat_);
          continue;
        }
        if (name == 'Dialogue') {
          const values = value.split(SsaTextParser.valuesFormat_);
          const data = {};
          for (let c = 0; c < eventColumns.length && c < values.length; c++) {
            data[eventColumns[c]] = values[c];
          }

          const startTime = SsaTextParser.parseTime_(data['Start']);
          const endTime = SsaTextParser.parseTime_(data['End']);

          // Note: Normally, you should take the "Text" field, but if it
          // has a comma, it fails.
          const payload = values.slice(eventColumns.length - 1).join(',')
              .replace(/\\N/g, '\n') // '\n' for new line
              .replace(/\{[^}]+\}/g, ''); // {\pos(400,570)}

          const cue = new shaka.text.Cue(startTime, endTime, payload);

          const styleName = data['Style'];
          const styleData = styles.find((s) => s['Name'] == styleName);
          if (styleData) {
            SsaTextParser.addStyle_(cue, styleData);
          }
          cues.push(cue);
          continue;
        }
      }
    }

    return cues;
  }

  /**
   * Adds applicable style properties to a cue.
   *
   * @param {shaka.extern.Cue} cue
   * @param {Object} style
   * @private
   */
  static addStyle_(cue, style) {
    const Cue = shaka.text.Cue;
    const SsaTextParser = shaka.text.SsaTextParser;
    const fontFamily = style['Fontname'];
    if (fontFamily) {
      cue.fontFamily = fontFamily;
    }
    const fontSize = style['Fontsize'];
    if (fontSize) {
      cue.fontSize = fontSize + 'px';
    }
    const color = style['PrimaryColour'];
    if (color) {
      const ccsColor = SsaTextParser.parseSsaColor_(color);
      if (ccsColor) {
        cue.color = ccsColor;
      }
    }
    const backgroundColor = style['BackColour'];
    if (backgroundColor) {
      const cssBackgroundColor = SsaTextParser.parseSsaColor_(backgroundColor);
      if (cssBackgroundColor) {
        cue.backgroundColor = cssBackgroundColor;
      }
    }
    const bold = style['Bold'];
    if (bold) {
      cue.fontWeight = Cue.fontWeight.BOLD;
    }
    const italic = style['Italic'];
    if (italic) {
      cue.fontStyle = Cue.fontStyle.ITALIC;
    }
    const underline = style['Underline'];
    if (underline) {
      cue.textDecoration.push(Cue.textDecoration.UNDERLINE);
    }
    const letterSpacing = style['Spacing'];
    if (letterSpacing) {
      cue.letterSpacing = letterSpacing + 'px';
    }
    const alignment = style['Alignment'];
    if (alignment) {
      const alignmentInt = parseInt(alignment, 10);
      switch (alignmentInt) {
        case 1:
          cue.displayAlign = Cue.displayAlign.AFTER;
          cue.textAlign = Cue.textAlign.START;
          break;
        case 2:
          cue.displayAlign = Cue.displayAlign.AFTER;
          cue.textAlign = Cue.textAlign.CENTER;
          break;
        case 3:
          cue.displayAlign = Cue.displayAlign.AFTER;
          cue.textAlign = Cue.textAlign.END;
          break;
        case 5:
          cue.displayAlign = Cue.displayAlign.BEFORE;
          cue.textAlign = Cue.textAlign.START;
          break;
        case 6:
          cue.displayAlign = Cue.displayAlign.BEFORE;
          cue.textAlign = Cue.textAlign.CENTER;
          break;
        case 7:
          cue.displayAlign = Cue.displayAlign.BEFORE;
          cue.textAlign = Cue.textAlign.END;
          break;
        case 9:
          cue.displayAlign = Cue.displayAlign.CENTER;
          cue.textAlign = Cue.textAlign.START;
          break;
        case 10:
          cue.displayAlign = Cue.displayAlign.CENTER;
          cue.textAlign = Cue.textAlign.CENTER;
          break;
        case 11:
          cue.displayAlign = Cue.displayAlign.CENTER;
          cue.textAlign = Cue.textAlign.END;
          break;
      }
    }
    const opacity = style['AlphaLevel'];
    if (opacity) {
      cue.opacity = parseFloat(opacity);
    }
  }

  /**
   * Parses a SSA color .
   *
   * @param {string} colorString
   * @return {?string}
   * @private
   */
  static parseSsaColor_(colorString) {
    // The SSA V4+ color can be represented in hex (&HAABBGGRR) or in decimal
    // format (byte order AABBGGRR) and in both cases the alpha channel's
    // value needs to be inverted as in case of SSA the 0xFF alpha value means
    // transparent and 0x00 means opaque
    /** @type {number} */
    const abgr = parseInt(colorString.replace('&H', ''), 16);
    if (abgr >= 0) {
      const a = ((abgr >> 24) & 0xFF) ^ 0xFF; // Flip alpha.
      const alpha = a / 255;
      const b = (abgr >> 16) & 0xFF;
      const g = (abgr >> 8) & 0xFF;
      const r = abgr & 0xff;
      return 'rgba(' + r + ',' + g + ',' + b + ',' + alpha + ')';
    }
    return null;
  }

  /**
   * Parses a SSA time from the given parser.
   *
   * @param {string} string
   * @return {number}
   * @private
   */
  static parseTime_(string) {
    const SsaTextParser = shaka.text.SsaTextParser;
    const match = SsaTextParser.timeFormat_.exec(string);
    const hours = match[1] ? parseInt(match[1].replace(':', ''), 10) : 0;
    const minutes = parseInt(match[2], 10);
    const seconds = parseFloat(match[3]);
    return hours * 3600 + minutes * 60 + seconds;
  }
};

/**
 * @const
 * @private {!RegExp}
 * @example [V4 Styles]\nFormat: Name\nStyle: DefaultVCD
 */
shaka.text.SsaTextParser.ssaContent_ =
    /^\s*\[([^\]]+)\]\r?\n([\s\S]*)/;

/**
 * @const
 * @private {!RegExp}
 * @example Style: DefaultVCD,...
 */
shaka.text.SsaTextParser.lineParts_ =
    /^\s*([^:]+):\s*(.*)/;

/**
 * @const
 * @private {!RegExp}
 * @example Style: DefaultVCD,...
 */
shaka.text.SsaTextParser.valuesFormat_ = /\s*,\s*/;

/**
 * @const
 * @private {!RegExp}
 * @example 0:00:01.1 or 0:00:01.18 or 0:00:01.180
 */
shaka.text.SsaTextParser.timeFormat_ =
    /^(\d+:)?(\d{1,2}):(\d{1,2}(?:[.]\d{1,3})?)?$/;

shaka.text.TextEngine.registerParser(
    'text/x-ssa', () => new shaka.text.SsaTextParser());