src/loader/fragment.ts

import { buildAbsoluteURL } from 'url-toolkit';
import { logger } from '../utils/logger';
import LevelKey from './level-key';
import LoadStats from './load-stats';
import AttrList from '../utils/attr-list';
import type {
  FragmentLoaderContext,
  Loader,
  PlaylistLevelType,
} from '../types/loader';

export enum ElementaryStreamTypes {
  AUDIO = 'audio',
  VIDEO = 'video',
  AUDIOVIDEO = 'audiovideo',
}

interface ElementaryStreamInfo {
  startPTS: number;
  endPTS: number;
  startDTS: number;
  endDTS: number;
  partial?: boolean;
}

type ElementaryStreams = Record<
  ElementaryStreamTypes,
  ElementaryStreamInfo | null
>;

export class BaseSegment {
  private _byteRange: number[] | null = null;
  private _url: string | null = null;

  // baseurl is the URL to the playlist
  public readonly baseurl: string;
  // relurl is the portion of the URL that comes from inside the playlist.
  public relurl?: string;
  // Holds the types of data this fragment supports
  public elementaryStreams: ElementaryStreams = {
    [ElementaryStreamTypes.AUDIO]: null,
    [ElementaryStreamTypes.VIDEO]: null,
    [ElementaryStreamTypes.AUDIOVIDEO]: null,
  };

  constructor(baseurl: string) {
    this.baseurl = baseurl;
  }

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

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

    return this._byteRange;
  }

  get byteRangeStartOffset(): number {
    return this.byteRange[0];
  }

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

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

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

export default class Fragment extends BaseSegment {
  private _decryptdata: LevelKey | null = null;

  public rawProgramDateTime: string | null = null;
  public programDateTime: number | null = null;
  public tagList: Array<string[]> = [];

  // EXTINF has to be present for a m38 to be considered valid
  public duration: number = 0;
  // sn notates the sequence number for a segment, and if set to a string can be 'initSegment'
  public sn: number | 'initSegment' = 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
  public levelkey?: LevelKey;
  // A string representing the fragment type
  public readonly type: PlaylistLevelType;
  // A reference to the loader. Set while the fragment is loading, and removed afterwards. Used to abort fragment loading
  public loader: Loader<FragmentLoaderContext> | null = null;
  // The level/track index to which the fragment belongs
  public level: number = -1;
  // The continuity counter of the fragment
  public cc: number = 0;
  // The starting Presentation Time Stamp (PTS) of the fragment. Set after transmux complete.
  public startPTS?: number;
  // The ending Presentation Time Stamp (PTS) of the fragment. Set after transmux complete.
  public endPTS?: number;
  // The latest Presentation Time Stamp (PTS) appended to the buffer.
  public appendedPTS?: number;
  // The starting Decode Time Stamp (DTS) of the fragment. Set after transmux complete.
  public startDTS!: number;
  // The ending Decode Time Stamp (DTS) of the fragment. Set after transmux complete.
  public endDTS!: number;
  // The start time of the fragment, as listed in the manifest. Updated after transmux complete.
  public start: number = 0;
  // Set by `updateFragPTSDTS` in level-helper
  public deltaPTS?: number;
  // The maximum starting Presentation Time Stamp (audio/video PTS) of the fragment. Set after transmux complete.
  public maxStartPTS?: number;
  // The minimum ending Presentation Time Stamp (audio/video PTS) of the fragment. Set after transmux complete.
  public minEndPTS?: number;
  // Load/parse timing information
  public stats: LoadStats = new LoadStats();
  public urlId: number = 0;
  public data?: Uint8Array;
  // A flag indicating whether the segment was downloaded in order to test bitrate, and was not buffered
  public bitrateTest: boolean = false;
  // #EXTINF  segment title
  public title: string | null = null;

  constructor(type: PlaylistLevelType, baseurl: string) {
    super(baseurl);
    this.type = type;
  }

  get decryptdata(): LevelKey | null {
    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
        ) {
          logger.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 end(): number {
    return this.start + this.duration;
  }

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

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

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

    return this.programDateTime + duration * 1000;
  }

  get encrypted() {
    // At the m3u8-parser level we need to add support for manifest signalled keyformats
    // when we want the fragment to start reporting that it is encrypted.
    // Currently, keyFormat will only be set for identity keys
    if (this.decryptdata?.keyFormat && this.decryptdata.uri) {
      return true;
    }

    return false;
  }

  /**
   * 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: number): Uint8Array {
    const 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: LevelKey,
    segmentNumber: number
  ): LevelKey {
    let decryptdata = levelkey;

    if (levelkey?.method === 'AES-128' && levelkey.uri && !levelkey.iv) {
      decryptdata = LevelKey.fromURI(levelkey.uri);
      decryptdata.method = levelkey.method;
      decryptdata.iv = this.createInitializationVector(segmentNumber);
      decryptdata.keyFormat = 'identity';
    }

    return decryptdata;
  }

  setElementaryStreamInfo(
    type: ElementaryStreamTypes,
    startPTS: number,
    endPTS: number,
    startDTS: number,
    endDTS: number,
    partial: boolean = false
  ) {
    const { elementaryStreams } = this;
    const info = elementaryStreams[type];
    if (!info) {
      elementaryStreams[type] = {
        startPTS,
        endPTS,
        startDTS,
        endDTS,
        partial,
      };
      return;
    }

    info.startPTS = Math.min(info.startPTS, startPTS);
    info.endPTS = Math.max(info.endPTS, endPTS);
    info.startDTS = Math.min(info.startDTS, startDTS);
    info.endDTS = Math.max(info.endDTS, endDTS);
  }

  clearElementaryStreamInfo() {
    const { elementaryStreams } = this;
    elementaryStreams[ElementaryStreamTypes.AUDIO] = null;
    elementaryStreams[ElementaryStreamTypes.VIDEO] = null;
    elementaryStreams[ElementaryStreamTypes.AUDIOVIDEO] = null;
  }
}

export class Part extends BaseSegment {
  public readonly fragOffset: number = 0;
  public readonly duration: number = 0;
  public readonly gap: boolean = false;
  public readonly independent: boolean = false;
  public readonly relurl: string;
  public readonly fragment: Fragment;
  public readonly index: number;
  public stats: LoadStats = new LoadStats();

  constructor(
    partAttrs: AttrList,
    frag: Fragment,
    baseurl: string,
    index: number,
    previous?: Part
  ) {
    super(baseurl);
    this.duration = partAttrs.decimalFloatingPoint('DURATION');
    this.gap = partAttrs.bool('GAP');
    this.independent = partAttrs.INDEPENDENT
      ? partAttrs.bool('INDEPENDENT')
      : true;
    this.relurl = partAttrs.enumeratedString('URI') as string;
    this.fragment = frag;
    this.index = index;
    const byteRange = partAttrs.enumeratedString('BYTERANGE');
    if (byteRange) {
      this.setByteRange(byteRange, previous);
    }
    if (previous) {
      this.fragOffset = previous.fragOffset + previous.duration;
    }
  }

  get start(): number {
    return this.fragment.start + this.fragOffset;
  }

  get end(): number {
    return this.start + this.duration;
  }

  get loaded(): boolean {
    const { elementaryStreams } = this;
    return !!(
      elementaryStreams.audio ||
      elementaryStreams.video ||
      elementaryStreams.audiovideo
    );
  }
}