extract_transcript

Implementation Reference

• src/modules/transcript-extractor.js:10-48 (handler)

  Core handler function implementing the transcript extraction logic from YouTube videos using the 'youtube-transcript' library with API fallback.

  export async function extractTranscript(youtubeUrl, youtubeApiKey = null) {
    try {
      console.log(`Extracting transcript from: ${youtubeUrl}`);
      
      // Extract video ID from URL
      const videoId = extractVideoId(youtubeUrl);
      if (!videoId) {
        throw new Error("Invalid YouTube URL. Could not extract video ID.");
      }
      
      // Try to get transcript using youtube-transcript package
      try {
        const transcriptItems = await YoutubeTranscript.fetchTranscript(videoId);
        if (!transcriptItems || transcriptItems.length === 0) {
          throw new Error("No transcript available");
        }
        
        // Combine transcript segments into a single text
        const fullTranscript = transcriptItems
          .map(item => item.text)
          .join(' ')
          .replace(/\s+/g, ' '); // Clean up extra spaces
        
        return fullTranscript;
      } catch (error) {
        console.error("Error with primary transcript method:", error);
        
        // Fallback to YouTube API if available
        if (youtubeApiKey) {
          return await fetchTranscriptWithYouTubeAPI(videoId, youtubeApiKey);
        } else {
          throw new Error("Failed to extract transcript: " + error.message);
        }
      }
    } catch (error) {
      console.error("Transcript extraction error:", error);
      throw new Error(`Failed to extract transcript: ${error.message}`);
    }
  }

• src/server.js:74-110 (registration)

  MCP server tool registration for 'extract_transcript', including input schema, execution handler wrapper, and description.

  server.tool(
    "extract_transcript",
    { 
      youtubeUrl: z.string().url().describe("YouTube video URL")
    },
    async ({ youtubeUrl }) => {
      try {
        // Check if YouTube API key is set (if needed)
        if (!apiKeyManager.hasYouTubeKey()) {
          console.log("No YouTube API key set, will try without it");
        }
        
        const transcript = await extractTranscript(youtubeUrl, apiKeyManager.getYouTubeKey());
        return {
          content: [{ 
            type: "text", 
            text: JSON.stringify({
              success: true,
              transcript
            }, null, 2)
          }]
        };
      } catch (error) {
        return {
          content: [{ 
            type: "text", 
            text: JSON.stringify({
              success: false,
              error: error.message
            }, null, 2)
          }],
          isError: true
        };
      }
    },
    { description: "Extract transcript from a YouTube video" }
  );

• src/server.js:76-78 (schema)

  Zod schema defining the input parameter 'youtubeUrl' as a required URL string.

  { 
    youtubeUrl: z.string().url().describe("YouTube video URL")
  },

• src/modules/transcript-extractor.js:54-74 (helper)

  Helper function to parse YouTube video ID from various URL formats.

   */
  function extractVideoId(url) {
    try {
      const urlObj = new URL(url);
      
      // Standard YouTube URL (youtube.com/watch?v=VIDEO_ID)
      if (urlObj.hostname.includes('youtube.com')) {
        return urlObj.searchParams.get('v');
      }
      
      // Short YouTube URL (youtu.be/VIDEO_ID)
      if (urlObj.hostname === 'youtu.be') {
        return urlObj.pathname.substring(1);
      }
      
      return null;
    } catch (error) {
      console.error("Error extracting video ID:", error);
      return null;
    }
  }

• src/modules/transcript-extractor.js:81-104 (helper)

  Fallback helper for fetching transcript via YouTube Data API v3 (incomplete, notes OAuth2 needed).

   */
  async function fetchTranscriptWithYouTubeAPI(videoId, apiKey) {
    if (!apiKey) {
      throw new Error("YouTube API key not provided");
    }
    
    // First, get the caption track
    const captionUrl = `https://www.googleapis.com/youtube/v3/captions?part=snippet&videoId=${videoId}&key=${apiKey}`;
    
    const response = await fetch(captionUrl);
    if (!response.ok) {
      throw new Error(`YouTube API error: ${response.statusText}`);
    }
    
    const data = await response.json();
    
    if (!data.items || data.items.length === 0) {
      throw new Error("No captions available for this video");
    }
    
    // Note: Actually downloading the caption track requires OAuth2 authentication
    // which is beyond the scope of this example
    throw new Error("YouTube API fallback requires OAuth2 authentication");
  }