YouTube Transcript Extraction

Extract subtitles/transcripts from a YouTube video URL and save them as a local file.

Input YouTube URL: $ARGUMENTS

Step 1: Verify URL

Confirm the input is a valid YouTube URL (supports youtube.com/watch?v=, youtu.be/, and youtube.com/shorts/ formats). If no URL is provided via arguments, check the conversation context for a YouTube link.

Step 2: CLI Quick Extraction (Priority Attempt)

Use command-line tools to quickly extract subtitles.

2.1 Check Tool Availability

Execute which yt-dlp.

• If yt-dlp is found, proceed to 2.2.
• If yt-dlp is not found, skip to Step 3.

2.2 Get Video Title

yt-dlp --cookies-from-browser=chrome --get-title "[VIDEO_URL]"

• Tip: Always add --cookies-from-browser to avoid sign-in restrictions. Default to chrome.
• If it fails with a browser error (e.g., "Could not open Chrome"), ask the user to specify their available browser (e.g., firefox, safari, edge) and retry.

2.3 Download Subtitles

yt-dlp --cookies-from-browser=chrome --write-auto-sub --write-sub --sub-lang zh-Hans,zh-Hant,en --skip-download --output "<Video Title>.%(ext)s" "[VIDEO_URL]"

2.4 Convert to Plain Text

yt-dlp saves subtitles as .vtt or .srt files. Convert the downloaded file to plain Timestamp Text format:

1. Read the downloaded subtitle file (.vtt or .srt).
2. Strip VTT/SRT headers, styling tags, and duplicate lines.
3. Save as <Video Title>.txt with one Timestamp Text entry per line.

2.5 Verify Results

• Exit code 0: Convert and save the subtitle file, then report completion.
• Exit code non-0:
  • If error is related to browser/cookies, ask user for correct browser and retry.
  • If other errors (e.g., video unavailable), proceed to Step 3.

Step 3: Browser Automation (Fallback)

When the CLI method fails or yt-dlp is missing, use Chrome DevTools MCP to extract subtitles via browser UI automation.

3.1 Check Tool Availability

Check if Chrome DevTools MCP tools are available (look for tools matching chrome__new_page or similar).

If Chrome DevTools MCP is not available and yt-dlp was not found in Step 2, stop and notify the user: "Unable to proceed. Please either install yt-dlp (for fast CLI extraction) or configure Chrome DevTools MCP (for browser automation)."

3.2 Open Video Page

Use Chrome DevTools MCP new_page to open the video URL.

3.3 Analyze Page State

Use Chrome DevTools MCP take_snapshot to read the page accessibility tree.

3.4 Expand Video Description

The "Show transcript" button is usually hidden within the collapsed description area.

1. Search the snapshot for a button labeled "...more", "...更多", or "Show more" (in the description block below the video title).
2. Use Chrome DevTools MCP click to click that button.

3.5 Open Transcript Panel

1. Use Chrome DevTools MCP take_snapshot to get the updated UI.
2. Search for a button labeled "Show transcript", "显示转录稿", or "内容转文字".
3. Use Chrome DevTools MCP click to click that button.
4. If the button is not found, the video may not have a transcript available — notify the user and stop.

3.6 Extract Content via DOM

Directly reading the accessibility tree for long transcript lists is slow and token-heavy. Use Chrome DevTools MCP evaluate_script to run this JavaScript instead:

() => {
  const segments = document.querySelectorAll("ytd-transcript-segment-renderer");
  if (!segments.length) return "BUFFERING";
  return Array.from(segments)
    .map((seg) => {
      const time = seg.querySelector(".segment-timestamp")?.innerText.trim();
      const text = seg.querySelector(".segment-text")?.innerText.trim();
      return `${time} ${text}`;
    })
    .join("\n");
};

If it returns "BUFFERING", wait a few seconds and retry (up to 3 attempts).

3.7 Save and Cleanup

1. Save the extracted text as <Video Title>.txt.
2. Use Chrome DevTools MCP close_page to release resources.

Output Requirements

• Save the subtitle file to the current working directory.
• Filename format: <Video Title>.txt
• File content format: Each line should be Timestamp Subtitle Text.
• Report upon completion: file path, subtitle language, and total number of lines.