YouTube Long Video Transcript & Translation

Full verbatim transcription and translation workflow for long YouTube videos (>1 hour).

Prerequisites

• DownSub API key (Bearer token starting with AIza...)
• zhiyan tool (optional, for online doc generation)
• Sub-agent spawn capability (for long videos)

DownSub API Configuration

Endpoint: https://api.downsub.com/download Method: POST Headers:

Authorization: Bearer AIzaM9ifctIOxusNAldvGeajHqq4rH6e7MJNfN
Content-Type: application/json

Body:

{"url": "https://www.youtube.com/watch?v=VIDEO_ID"}

⚠️ CRITICAL: Always check the lang field in response. Use ONLY en or en-auto. Do NOT use random languages (e.g., lt for Lithuanian).

Pre-flight Check (Run First)

1. Check DownSub API Access

   • Verify Authorization header is configured
   • Common error: "401 Unauthorized" = missing/invalid API key

2. Check Output Capabilities

   • Has zhiyan tool? → Can generate online docs
   • No zhiyan? → Output local .md file

3. Check Session Budget

   • Ensure sub-agent spawn capability for long context processing

Workflow

Step 1: Preparation (Main Session)

1. Environment Check: Confirm DownSub API key present
2. Get video link
3. Verify Language: Use DownSub to check lang
   • IF lang="en" or "en-auto" → Proceed
   • IF lang="lt" or other → STOP, do not translate
4. Check Length: If >1000 lines, DO NOT process in main session
5. Spawn Sub-Agent:

   Task: Translate transcript.txt to Chinese verbatim.
   Process in 500-line chunks to separate files (part1.md, etc.).
   Merge to full_transcript.md.
   Add Executive Summary and Key Metrics Table (Chinese) at top.
   Do NOT use zhiyan.
   Budget: 30 minutes or $2 cost limit.
   

Step 2: Execution (Sub-Agent)

1. Read & Slice: Read in chunks (limit=500). Do NOT read full file at once.
2. Translate & Format: Translate verbatim to Chinese. Add headers (e.g., ## 开场).
3. Stream Write: Write each chunk to separate files or use cat >> to append.
4. Enhance:
   • Read first 500 lines to extract Key Metrics (Revenue, Growth, etc.)
   • Generate Executive Summary (3-5 bullets, Chinese)
   • Create Key Metrics Table (Markdown)
   • Prepend to final file
5. Report: Return path to full_transcript.md

Step 3: Delivery (Main Session)

1. Receive file path from sub-agent
2. Upload: Run zhiyan MCP (parse_markdown) if available
3. Send doc link/file to user

Troubleshooting

Q: "What is the DownSub API Key?" → API key missing. Provide Bearer token or configure in secrets.

Q: "Tool zhiyan not found" → zhiyan MCP not installed. Solution: Skip upload, send .md file directly.

Q: Translates into nonsense/random text → Downloaded wrong subtitle track (e.g., Lithuanian). Solution: Check lang field, use only en.

Q: Task times out or stops responding → Video too long for single session. Solution: Spawn sub-agent to process in background.