hjplayer/src/Loaders/Fragment.ts

hjplayer, a HTML5 Player, can play flv and hls by Media Source Extension, based on typescript;

import URLToolkit from 'url-toolkit';
import logger from '../Utils/Logger';
import LevelKey from '../Parser/LevelKey';
import { PlaylistLevelType } from '../Interfaces/loader';

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

export default class Fragment {
    Tag: string = 'Fragment'

    private _url: string | null = null

    private _byteRange: number[] | null = null

    private _decryptdata: LevelKey | null = null

    // Holds the types of data this fragment supports
    private _elementaryStreams: Record<ElementaryStreamTypes, boolean> = {
        [ElementaryStreamTypes.AUDIO]: false,
        [ElementaryStreamTypes.VIDEO]: false
    }

    // deltaPTS tracks the change in presentation timestamp between fragments
    public deltaPTS: number = 0

    public rawProgramDateTime: string | null = null

    public programDateTime: number | null = null

    public title: string | null = null

    public tagList: Array<string[]> = []

    // 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
    public cc!: number

    public type!: PlaylistLevelType

    // relurl is the portion of the URL that comes from inside the playlist.
    public relurl!: string

    // baseurl is the URL to the playlist
    public baseurl!: string

    // EXTINF has to be present for a m3u8 to be considered valid
    public duration!: number

    // When this segment starts in the timeline
    public start!: number

    // sn notates the sequence number for a segment, and if set to a string can be 'initSegment'
    public sn: number | 'initSegment' = 0

    public urlId: number = 0

    // level matches this fragment to a index playlist
    public level: number = 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

    // TODO(typescript-xhrloader)
    public loader: any

    // setByteRange converts a EXT-X-BYTERANGE attribute into a two element array
    setByteRange(value: string, previousFrag?: Fragment) {
        const params = value.split('@', 2);
        const byteRange: number[] = [];
        if(params.length === 1) {
            byteRange[0] = previousFrag ? previousFrag.byteRangeEndOffset : 0;
        } else {
            byteRange[0] = parseInt(params[1], 10);
        }
        byteRange[1] = parseInt(params[0], 10) + 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(): number[] {
        if(!this._byteRange) {
            return [];
        }

        return this._byteRange;
    }

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

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

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

        if(!this._decryptdata && this.levelkey) {
            let { sn } = this;
            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(
                        this.Tag,
                        `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;
        }

        const 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: ElementaryStreamTypes) {
        this._elementaryStreams[type] = true;
    }

    /**
     * @param {ElementaryStreamTypes} type
     */
    hasElementaryStream(type: ElementaryStreamTypes) {
        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: 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 && levelkey.method && levelkey.uri && !levelkey.iv) {
            decryptdata = new LevelKey(levelkey.baseuri, levelkey.reluri);
            decryptdata.method = levelkey.method;
            decryptdata.iv = this.createInitializationVector(segmentNumber);
        }

        return decryptdata;
    }
}