What it does

Self-hosted Slack-alternative sink: Mattermost's incoming webhooks accept the same JSON shape as Slack. The peepshow attachment has fields for strategy, codec, duration, resolution, director, studio, and can embed frame images when `MATTERMOST_IMAGE_BASE` is set.

When to reach for it

Teams on self-hosted Mattermost instead of Slack
Per-channel routing via `MATTERMOST_CHANNEL` to reuse one webhook across many rooms
Embed a grid of frames in the main channel when served from a public base URL

Install

npm i -g peepshow

Use it

MATTERMOST_WEBHOOK_URL=https://mm.example.com/hooks/... \
peepshow ./clip.mp4 --sink mattermost

Make it automatic

peepshow sinks add mattermost
peepshow sinks add mattermost --when extension=mp4,mov
peepshow sinks add mattermost --when path=/Volumes/Work/

Configuration

MATTERMOST_WEBHOOK_URL Incoming-webhook URL. required
MATTERMOST_CHANNEL Override target channel (`town-square`, `@alice`, `~announcements`).
MATTERMOST_USERNAME Override bot display name.
MATTERMOST_ICON_URL Override bot avatar URL.
MATTERMOST_IMAGE_BASE URL prefix for frame image attachments.
MATTERMOST_MAX_IMAGES Max image attachments. Default `4`.

Use with an LLM agent

Every peepshow sink reads its config from env vars and receives a single JSON payload on stdin. An LLM agent (Claude Code, Cursor, Windsurf, Gemini, Codex) can drive the Mattermost sink automatically when three things are true:

the env vars below are exported in the agent's shell (or a project .env it can load),
the peepshow CLI is on PATH — install with npm i -g peepshow,
a peepshow auto-sink is registered for the run (optional but recommended — makes invocation zero-argument).

1. Set the environment

# Add to ~/.zshrc, ~/.bashrc, or a project .env the agent can load
export MATTERMOST_WEBHOOK_URL="..."

2. Register as an auto-sink

peepshow sinks add mattermost
peepshow sinks add mattermost --when extension=mp4,mov

3. Example LLM session

You → drop a .mov into Claude Code.
Claude → auto-invokes /peepshow:slides ./clip.mov. peepshow extracts frames + audio, the Mattermost sink forwards the run to the configured channel. Claude replies with a summary and a link to the created record.

The transcript snippet is posted alongside the frames as a secondary message.

Write your own

A sink is any executable that reads the --emit json payload on stdin. Shell, Node, Python, Go — the spec's in docs/PLUGINS.md. Register persistent ones with peepshow sinks add-cmd 'your-command'.

Mattermost — POST every run to a Mattermost webhook.