youtube-fetch

Overview

This skill retrieves YouTube video content (metadata and transcripts). CC's built-in WebFetch only gets the page shell, not what the video says (a PreToolUse hook blocks it for YouTube).

Primary path — the genesis web_fetch MCP tool. Call mcp__genesis-health__web_fetch with the video URL (or urls=[...] for a batch). For a YouTube video it runs yt-dlp in Python and returns the title, channel, description and transcript, preferring captions in the video's own language (manual over automatic; a track chosen without language evidence is labelled provenance: unknown), with a Transcript source line and a caption field giving the track and its provenance. It needs no shell, so it also works in background sessions. The video text arrives inside <external-content> markers, because captions and descriptions are written by whoever uploaded the video. If it reports youtube_error, read the error; the rest of the result is the page's title and description. In a urls=[...] batch, a video's entry is its transcript result when yt-dlp succeeds and the ordinary page entry when it does not.

Fallback — yt-dlp via Bash (foreground sessions only), when web_fetch is unavailable or you need a specific track. The workflow below is that fallback. yt-dlp is a Genesis dependency, installed in the venv.

Workflow (Bash fallback)

1. Ensure yt-dlp is available (install if needed):

   which yt-dlp || pip install yt-dlp
   

2. Fetch metadata for each video:

   yt-dlp --skip-download --print '%(title)s|||%(uploader)s|||%(description)s' 'VIDEO_URL'
   

3. Fetch the auto-generated transcript. Request both English tracks and prefer en-orig:

   VID='VIDEO_ID'   # <- substitute the real 11-char video id
   mkdir -p ~/tmp/yt-transcripts
   rm -f ~/tmp/yt-transcripts/"$VID".*.vtt        # drop any earlier run's files
   yt-dlp --write-auto-sub --skip-download --sub-langs "en-orig,en" -o "$HOME/tmp/yt-transcripts/%(id)s" 'VIDEO_URL'
   ls ~/tmp/yt-transcripts/ | grep -F -- "$VID"
   

   The rm -f is load-bearing, not tidiness: that directory persists across runs and across videos, so a stale $VID.en-orig.vtt from an earlier fetch would satisfy step 4's preference check even when THIS fetch failed or returned only en — you would clean an old transcript and never see an error. grep -F -- because a video id may begin with -, which grep would otherwise read as options. YouTube may serve two English auto-caption tracks — en-orig ("English (Original)") and en ("English"). Usually they are the same resource. Observed 2026-09 on one video: the two were served with different cue segmentation, and the closing lines differed in wording ("subscribe" vs "subscription") — that wording difference is direct evidence of a different transcription. The same video served byte-identical tracks hours later. Cause unknown; requesting both and preferring en-orig costs one extra small download and is free insurance either way.

   en-orig exists only where the video's original audio is English. On a foreign-language video there is no en-orig, and en is a machine TRANSLATION with nothing in the file marking it as one. A requested track that does not exist is skipped silently — check the ls, and see step 6 if nothing was written.

4. Clean the VTT into plain text. Do the file-preference and the clean in one Bash call — shell variables do not survive between calls:

   VID='VIDEO_ID'   # <- substitute the real 11-char video id
   VTT="$HOME/tmp/yt-transcripts/$VID.en-orig.vtt"
   [ -f "$VTT" ] || VTT="$HOME/tmp/yt-transcripts/$VID.en.vtt"
   [ -f "$VTT" ] || { echo "no English VTT for $VID — see step 6" >&2; exit 1; }
   sed '/^WEBVTT/d;/^Kind:/d;/^Language:/d;/^[0-9][0-9]:[0-9][0-9]:[0-9][0-9]\.[0-9]* -->/d;s/<[^>]*>//g;/^[[:space:]]*$/d' "$VTT" | awk '!seen[$0]++'
   

   The ORDER is the whole point, and each stage bit a previous version:

   • Control-line deletes run FIRST, on raw text. A real WEBVTT/Kind:/ Language:/cue-header line carries no tags, so on raw text those predicates are unambiguous. Strip tags first and a genuine caption can be mistaken for a control line and deleted — measured: <c>Language: Python is the topic</c> and <00:00:01.500><c>10:30</c> is the deadline were both destroyed by a strip-first ordering and both survive this one.
   • The cue-header pattern is anchored to the full HH:MM:SS.mmm --> shape rather than a bare ^[0-9][0-9]:[0-9][0-9], so a caption that merely starts with a clock time is not eaten.
   • Tag-strip next, blank-delete LAST. /^[[:space:]]*$/d, not /^$/d — a VTT carries BOTH truly-empty lines (the cue separator) and single-space lines (the first line of a cue payload); the plain form leaves the latter. Running it last also collapses any line that became empty once its markup was stripped.
   • The [ -f ] guard matters: without it a missing VTT makes sed write one stderr line while the pipeline still exits 0 (the status is awk's), so the failure looks like an empty transcript rather than an error.

   The awk de-dupes the rolling caption lines. It is whole-FILE, not adjacent, so a line genuinely repeated later in the talk is dropped too — and it is line-based, so a phrase split across a cue boundary will not survive a grep of the result. Flatten with tr '\n' ' ' | tr -s ' ' before searching for phrases, and treat a word-count delta between two tracks as suggestive only: different cue segmentation changes what de-dupes, independently of content.

5. If the transcript is too large to read at once, pipe through head -N / tail -n +N to read in chunks.

6. If no English track was written, DO NOT just drop --sub-langs — omitting it narrows the request to a single English-first track rather than broadening it (measured: it writes one en file even when a dozen languages exist). List what the video has, then request one language:

   # the listing runs to thousands of lines on a translated video — the real tracks
   # are at the top, so cap it rather than dumping it into the session
   yt-dlp --list-subs --skip-download 'VIDEO_URL' 2>&1 | head -45
   yt-dlp --write-auto-sub --skip-download --sub-langs "<lang>" -o "$HOME/tmp/yt-transcripts/%(id)s" 'VIDEO_URL'
   

   Pick from the "Available automatic captions" section — --write-auto-sub only fetches those. For a track listed under "Available subtitles" (human/community), swap in --write-sub. Then clean it with step 4, substituting your <lang> for en-orig/en in the two VTT= lines.

   Avoid --sub-langs all: it requests every translation pair the video exposes, which is hundreds to thousands of tracks.

Output Format

Present results per video as:

### Video: [Title]
**Channel:** [Uploader]
**URL:** [Original URL]

**Description:**
[Video description text]

**Transcript:**
[Cleaned transcript text, or summary if too long for context]

Parallel Processing

When multiple YouTube URLs are provided, run all metadata fetches in parallel (separate Bash calls in one message), then all transcript downloads in parallel. Process sequentially only if outputs depend on each other. Note --sub-langs "en-orig,en" writes up to TWO files per video, and the en-orig preference in step 4 must be resolved PER VIDEO, inside the same Bash call that cleans that video — one shared VTT variable across a batch will clean the wrong file.

Examples

Single Video

Input: "What does this video talk about? https://youtu.be/abc123"

Action: Call web_fetch with the URL; return its metadata and transcript. (Bash fallback: steps 1-4.)

Batch

Input: User provides 4 YouTube URLs for research compilation.

Action: Fetch all 4 metadata calls in parallel, then all 4 transcript downloads in parallel, then clean and return.

No Captions Available

Input: A video with no auto-generated subtitles.

Action: Follow step 6 — list the available tracks, fetch one in a language you can work with, and clean it with step 4. Only if no usable track exists, report that and return metadata and description only.