av/cmd/mjpeg-player/hlsjs/loader/fragment.js

/*
AUTHOR
  Trek Hopton <trek@ausocean.org>

LICENSE
  This file is Copyright (C) 2020 the Australian Ocean Lab (AusOcean)

  It is free software: you can redistribute it and/or modify them
  under the terms of the GNU General Public License as published by the
  Free Software Foundation, either version 3 of the License, or (at your
  option) any later version.

  It is distributed in the hope that it will be useful, but WITHOUT
  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
  for more details.

  You should have received a copy of the GNU General Public License in gpl.txt.
  If not, see http://www.gnu.org/licenses.

  For hls.js Copyright notice and license, see LICENSE file.
*/

import URLToolkit from '../../url-toolkit/url-toolkit.js';
import LevelKey from './level-key.js';

export const ElementaryStreamTypes = {
  AUDIO: 'audio',
  VIDEO: 'video'
}

export default class Fragment {
  constructor() {
    this._url = null;
    this._byteRange = null;
    this._decryptdata = null;

    // Holds the types of data this fragment supports
    this._elementaryStreams = {
      [ElementaryStreamTypes.AUDIO]: false,
      [ElementaryStreamTypes.VIDEO]: false
    };

    // deltaPTS tracks the change in presentation timestamp between fragments
    this.deltaPTS = 0;

    this.rawProgramDateTime = null;
    this.programDateTime = null;
    this.title = null;
    this.tagList = [];

    // TODO: Move at least baseurl to constructor.
    // Currently we do a two-pass construction as use the Fragment class almost like a object for holding parsing state.
    // It may make more sense to just use a POJO to keep state during the parsing phase.
    // Have Fragment be the representation once we have a known state?
    // Something to think on.

    // Discontinuity Counter
    this.cc;
    this.type;
    // relurl is the portion of the URL that comes from inside the playlist.
    this.relurl;
    // baseurl is the URL to the playlist
    this.baseurl;
    // EXTINF has to be present for a m3u8 to be considered valid
    this.duration;
    // When this segment starts in the timeline
    this.start;
    // sn notates the sequence number for a segment, and if set to a string can be 'initSegment'
    this.sn = 0;

    this.urlId = 0;
    // level matches this fragment to a index playlist
    this.level = 0;
    // levelkey is the EXT-X-KEY that applies to this segment for decryption
    // core difference from the private field _decryptdata is the lack of the initialized IV
    // _decryptdata will set the IV for this segment based on the segment number in the fragment
    this.levelkey;

    // TODO(typescript-xhrloader)
    this.loader;
  }

  // setByteRange converts a EXT-X-BYTERANGE attribute into a two element array
  setByteRange(value, previousFrag) {
    const params = value.split('@', 2);
    const byteRange = [];
    if (params.length === 1) {
      byteRange[0] = previousFrag ? previousFrag.byteRangeEndOffset : 0;
    } else {
      byteRange[0] = parseInt(params[1]);
    }
    byteRange[1] = parseInt(params[0]) + byteRange[0];
    this._byteRange = byteRange;
  }

  get url() {
    if (!this._url && this.relurl) {
      this._url = URLToolkit.buildAbsoluteURL(this.baseurl, this.relurl, { alwaysNormalize: true });
    }

    return this._url;
  }

  set url(value) {
    this._url = value;
  }

  get byteRange() {
    if (!this._byteRange) {
      return [];
    }

    return this._byteRange;
  }

  /**
   * @type {number}
   */
  get byteRangeStartOffset() {
    return this.byteRange[0];
  }

  get byteRangeEndOffset() {
    return this.byteRange[1];
  }

  get decryptdata() {
    if (!this.levelkey && !this._decryptdata) {
      return null;
    }

    if (!this._decryptdata && this.levelkey) {
      let sn = this.sn;
      if (typeof sn !== 'number') {
        // We are fetching decryption data for a initialization segment
        // If the segment was encrypted with AES-128
        // It must have an IV defined. We cannot substitute the Segment Number in.
        if (this.levelkey && this.levelkey.method === 'AES-128' && !this.levelkey.iv) {
          console.warn(`missing IV for initialization segment with method="${this.levelkey.method}" - compliance issue`);
        }

        /*
        Be converted to a Number.
        'initSegment' will become NaN.
        NaN, which when converted through ToInt32() -> +0.
        ---
        Explicitly set sn to resulting value from implicit conversions 'initSegment' values for IV generation.
        */
        sn = 0;
      }
      this._decryptdata = this.setDecryptDataFromLevelKey(this.levelkey, sn);
    }

    return this._decryptdata;
  }

  get endProgramDateTime() {
    if (this.programDateTime === null) {
      return null;
    }

    if (!Number.isFinite(this.programDateTime)) {
      return null;
    }

    let duration = !Number.isFinite(this.duration) ? 0 : this.duration;

    return this.programDateTime + (duration * 1000);
  }

  get encrypted() {
    return !!((this.decryptdata && this.decryptdata.uri !== null) && (this.decryptdata.key === null));
  }

  /**
   * @param {ElementaryStreamTypes} type
   */
  addElementaryStream(type) {
    this._elementaryStreams[type] = true;
  }

  /**
   * @param {ElementaryStreamTypes} type
   */
  hasElementaryStream(type) {
    return this._elementaryStreams[type] === true;
  }

  /**
   * Utility method for parseLevelPlaylist to create an initialization vector for a given segment
   * @param {number} segmentNumber - segment number to generate IV with
   * @returns {Uint8Array}
   */
  createInitializationVector(segmentNumber) {
    let uint8View = new Uint8Array(16);

    for (let i = 12; i < 16; i++) {
      uint8View[i] = (segmentNumber >> 8 * (15 - i)) & 0xff;
    }

    return uint8View;
  }

  /**
   * Utility method for parseLevelPlaylist to get a fragment's decryption data from the currently parsed encryption key data
   * @param levelkey - a playlist's encryption info
   * @param segmentNumber - the fragment's segment number
   * @returns {LevelKey} - an object to be applied as a fragment's decryptdata
   */
  setDecryptDataFromLevelKey(levelkey, segmentNumber) {
    let decryptdata = levelkey;

    if (levelkey && levelkey.method && levelkey.uri && !levelkey.iv) {
      decryptdata = new LevelKey(levelkey.baseuri, levelkey.reluri);
      decryptdata.method = levelkey.method;
      decryptdata.iv = this.createInitializationVector(segmentNumber);
    }

    return decryptdata;
  }
}