export const YoutubeTranscript = async (url: string, metadata = true) => { const RE_YOUTUBE = /(?:youtube\.com\/(?:[^\/]+\/.+\/|(?:v|e(?:mbed)?)\/|.*[?&]v=)|youtu\.be\/)([^"&?\/\s]{11})/i; const YouTubeKey = { apiKey: "INNERTUBE_API_KEY", serializedShareEntity: "serializedShareEntity", visitorData: "VISITOR_DATA", sessionId: "sessionId", clickTrackingParams: "clickTrackingParams", } as const; type ObjectValues = T[keyof T]; type YouTubeKeyRaw = ObjectValues; class YoutubeTranscriptError extends Error { constructor(message: string) { super(`[YoutubeTranscript] 🚨 ${message}`); } } interface TranscriptConfig { lang?: string; country?: string; } interface TranscriptSegment { text: string; duration: number; offset: number; } interface TranscriptData { responseContext: { serviceTrackingParams: { service: string; params: { key: string; value: string; }[]; }[]; mainAppWebResponseContext: { loggedOut: boolean; trackingParam: string; }; webResponseContextExtensionData: { hasDecorated: boolean; }; }; actions: { clickTrackingParams: string; updateEngagementPanelAction: { targetId: string; content: { transcriptRenderer: { body: { transcriptBodyRenderer: { cueGroups: { transcriptCueGroupRenderer: { formattedStartOffset: { simpleText: string; }; cues: { transcriptCueRenderer: { cue: { simpleText: string; }; startOffsetMs: string; durationMs: string; }; }[]; }; }[]; }; }; }; }; }; }[]; } /** * An extensible class to fetch a transcript from a given YouTube Video */ class YoutubeTranscript { /** * Fetch a transcript from a YouTube Video which includes the text and timestamp metadata * @param videoId Video url or video identifier * @param config Options for specifying a Country and Language ISO */ static async fetchTranscript( videoId: string, config?: TranscriptConfig, ): Promise { const identifier = this.extractVideoId(videoId); try { const textResponse = await fetch( `https://www.youtube.com/watch?v=${identifier}`, ); const body = await textResponse.text(); const apiKey = this.extractValue(body, YouTubeKey.apiKey); if (!apiKey || !apiKey.length) { throw new YoutubeTranscriptError( `Failed to extract ${YouTubeKey.apiKey}`, ); } const transcriptResponse = await fetch( `https://www.youtube.com/youtubei/v1/get_transcript?key=${apiKey}`, { method: "POST", body: JSON.stringify(this.generateRequest(body, config)), headers: { "content-type": "application/json", }, }, ); if (!transcriptResponse) { throw new YoutubeTranscriptError( "Empty response from transcript endpoint", ); } const transcriptData = await transcriptResponse.json(); return this.parseTranscriptData(transcriptData as TranscriptData); } catch (err) { throw new YoutubeTranscriptError(err); } } /** * Fetch only the transcript text from a YouTube Video * @param videoId Video url or video identifier * @param config Options for specifying a Country and Language ISO */ static async fetchTranscriptText( videoId: string, config?: TranscriptConfig, ): Promise { const segments = await this.fetchTranscript(videoId, config); let out = ""; for (const { text } of segments) { out += `${text} `; } return out.trimEnd(); } /** * Parse TranscriptData from the "get_transcript" endpoint * @param transcriptData TranscriptData returned by the "get_transcript" endpoint */ static parseTranscriptData(transcriptData: TranscriptData) { const { actions = [] } = transcriptData; const cueGroups = actions[0]?.updateEngagementPanelAction.content.transcriptRenderer.body .transcriptBodyRenderer.cueGroups; return cueGroups.map((cueGroup) => { const { cue, durationMs, startOffsetMs } = cueGroup.transcriptCueGroupRenderer.cues[0].transcriptCueRenderer; return { text: cue.simpleText, duration: parseInt(durationMs), offset: parseInt(startOffsetMs), }; }); } /** * Generate tracking params for YouTube API * @param page * @param config */ static generateRequest(page: string, config?: TranscriptConfig) { const clientScreenNonce = this.generateNonce(); const params = this.extractValue(page, YouTubeKey.serializedShareEntity); const visitorData = this.extractValue(page, YouTubeKey.visitorData); const sessionId = this.extractValue(page, YouTubeKey.sessionId); const clickTrackingParams = this.extractValue( page, YouTubeKey.clickTrackingParams, ); return { context: { client: { hl: config?.lang || "en", gl: config?.country || "US", visitorData, userAgent: "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_4) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/85.0.4183.83 Safari/537.36,gzip(gfe)", clientName: "WEB", clientVersion: "2.20200925.01.00", osName: "Macintosh", osVersion: "10_15_4", browserName: "Chrome", browserVersion: "85.0f.4183.83", screenWidthPoints: 1440, screenHeightPoints: 770, screenPixelDensity: 2, utcOffsetMinutes: 120, userInterfaceTheme: "USER_INTERFACE_THEME_LIGHT", connectionType: "CONN_CELLULAR_3G", }, request: { sessionId, internalExperimentFlags: [], consistencyTokenJars: [], }, user: {}, clientScreenNonce, clickTracking: { clickTrackingParams, }, }, params, }; } /** * Extract value from html page based on required key * @param page html page * @param key key name */ static extractValue(page: string, key: YouTubeKeyRaw) { return page.split(`"${key}":"`)[1]?.split(`"`)[0]; } /** * Extract video id from url or string * @param videoId video url or video id */ static extractVideoId(videoId: string) { if (videoId.length === 11) { return videoId; } const matchId = videoId.match(RE_YOUTUBE); if (matchId && matchId.length) { return matchId[1]; } throw new YoutubeTranscriptError("Malformed YouTube video url or ID."); } /** * Generate nonce for clientScreenNonce as part of YouTube API */ static generateNonce() { const rnd = Math.random().toString(); const alphabet = "ABCDEFGHIJKLMOPQRSTUVWXYZabcdefghjijklmnopqrstuvwxyz0123456789"; const jda = [ alphabet + "+/=", alphabet + "+/", alphabet + "-_=", alphabet + "-_.", alphabet + "-_", ]; const b = jda[3]; const a = []; for (let i = 0; i < rnd.length - 1; i++) { a.push(rnd[i].charCodeAt(i)); } let c = ""; let d = 0; let m, n, q, r, f, g; while (d < a.length) { f = a[d]; g = d + 1 < a.length; if (g) { m = a[d + 1]; } else { m = 0; } n = d + 2 < a.length; if (n) { q = a[d + 2]; } else { q = 0; } r = f >> 2; f = ((f & 3) << 4) | (m >> 4); m = ((m & 15) << 2) | (q >> 6); q &= 63; if (!n) { q = 64; if (!q) { m = 64; } } c += b[r] + b[f] + b[m] + b[q]; d += 3; } return c; } } if (metadata) return await YoutubeTranscript.fetchTranscript(url); return await YoutubeTranscript.fetchTranscriptText(url); };

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