signal-bot

A Signal group-chat bot that grabs videos from links people post (X/Twitter, Instagram, YouTube, TikTok, Reddit) and posts them back into the chat, plus a couple of toys for messing with the last video.

What it does

• Auto-download — watches every group message for a supported link and replies with the video. Powered by yt-dlp. Videos over 100 MB are auto re-encoded with ffmpeg to fit. YouTube is fetched as h264 up to 1080p, stepping down a resolution rung on longer videos so the merge lands under the Signal size limit without a re-encode; other hosts take their muxed rendition as-is.
• /speed [n] — re-posts the last video sped up n× (default 2×), pitch-shifted like tape. e.g. /speed 4, /speed 0.5.
• /rev — re-posts the last video reversed (audio too).
• /cookies (DM, admins only) — paste exported .instagram.com cookie lines to refresh Instagram auth without touching the server.

Supported links: x.com / twitter.com (and fxtwitter/vxtwitter/fixupx wrappers), instagram.com/reel|p, youtube.com / youtu.be / Shorts, TikTok, and Reddit (/comments/ permalinks, /s/ app share links, redd.it and v.redd.it shortlinks). Reddit posts with no video stay silent.

How it's wired

Signal  ──►  signal-cli-rest-api (json-rpc, :8080)  ──►  bot.py (signalbot lib)
                  [docker-compose.yml]                      [systemd service]
                                                                  │
                                                       yt-dlp + ffmpeg + cookies.txt

• bot.py connects to a signal-cli-rest-api daemon over a websocket in json-rpc mode.
• docker-compose.yml runs that daemon; the linked-account data lives in a ./signal-cli-data volume (gitignored — it holds private keys).
• signal-bot.service.example is the systemd unit that runs bot.py.

Setup

1. Run signal-cli-rest-api and link it as a device to your Signal account:

   docker compose up -d
   

   Then link via the QR at http://127.0.0.1:8080/v1/qrcodelink?device_name=bot (scan from Signal → Settings → Linked devices). Keep signal-cli up to date — an out-of-date signal-cli silently stops receiving messages when Signal changes its server protocol (getServerGuid must not be null in the logs); docker compose pull && docker compose up -d fixes it.

2. Python env:

   python3 -m venv venv
   venv/bin/pip install -r requirements.txt
   

   YouTube also needs Node >= 22 on PATH (for yt-dlp-ejs's challenge solver). If your distro only ships an older Node, install a standalone Node 22+ and point bot.py's _NODE22 at it. Note: YouTube cookies are deliberately withheld (_cookie_args) — sending account cookies forces yt-dlp onto a player client whose media URLs 403; cookieless YouTube requests work.

3. Cookies: copy cookies.txt.example to cookies.txt and fill in real exported cookies for the sites you want auth'd. (gitignored)

4. Service: copy signal-bot.service.example to signal-bot.service, set your user / phone number / paths, install it:

   sudo cp signal-bot.service /etc/systemd/system/
   sudo systemctl enable --now signal-bot
   

Notes

• The bot only acts in group chats (except /cookies, which is DM-only).
• Reply-targeting (e.g. "speed up this video") was intentionally dropped: Signal Desktop strips quote metadata from synced transcripts, so /speed and /rev always act on the last video seen in the group.