metamesh-plugin-still-extractor

MetaMesh container plugin. Grabs a representative frame out of a local video file and stores it as a content-addressed JPEG, referenced from the video record as still.

video file ──ffmpeg seek+decode──► frame ──WebDAV PUT──► /files/plugin/still-extractor/
                                                              │
                                                   midhash256 │
                                                              ▼
                                              meta-core:  still = <cid>

Why

Artwork on a local file otherwise comes from TMDB, and only when a title match succeeds. still (METADATA_KEYS.md §6.1) is the episode-level thumbnail slot — reserved for a future TMDB season-detail fetch, and until now written by nobody. This plugin gives it a first writer from the one source that never 404s and never depends on a match: the file itself.

A still is not a poster. Nothing gates on it, its absence is not an error, and this plugin never writes poster — a frame grab masquerading as real artwork would propagate to every peer that replicates the record. If a TMDB episode still ever lands on the record first, this plugin steps aside.

What it writes

Key	Value
still	midhash256 CID of the extracted JPEG

Nothing else — in particular no stillPath. /files/plugin is a meta-core watcher root, so the JPEG gets its own record and CID alias and LookupPathByCID resolves it through the reverse index. See the header comment in src/plugin.ts.

How a frame is chosen

1. Candidate offsets at 20 / 45 / 70 % of fileinfo/duration, clamped 2s away from both ends (the head is logos and black, the tail is credits).
2. At each offset, one ffmpeg run with input seeking (-ss before -i, so it Range-seeks over WebDAV instead of decoding from zero) and thumbnail=60, which picks the most representative of the next 60 frames.
3. The encoded JPEG is measured (mean + stddev of a 32×32 grayscale reduction). Black, blown-out and flat frames are rejected and the next offset is tried.
4. All candidates rejected → skipped, no field written.

The primary video stream is the largest one that looks like moving video — not 0:v:0, and not simply the largest. ffprobe reports attached cover art as codec_type=video, and a 600×900 cover out-measures a 640×480 film.

Configuration

Runtime config via meta-sort's plugin API (never plugins.yml):

curl -k -X PUT https://metasort-dev.localhost:8180/api/plugins/still-extractor/config \
  -H "Content-Type: application/json" \
  -d '{"seekPercents":"15,40,65","maxWidth":720,"jpegQuality":3}'

Key	Default	What
forceRecompute	false	Re-extract even when still is already set
seekPercents	"20,45,70"	Candidate offsets, as percentages of duration
maxWidth	640	Frame is scaled down to at most this width
jpegQuality	4	ffmpeg -q:v; lower is better quality
frameTimeoutMs	120000	Hard kill for one ffmpeg grab

Development

pnpm install && pnpm build
docker build -t metamesh-plugin-still-extractor:main .
./test.sh            # unit + fixture tests in a container with ffmpeg
./test.sh --shell    # interactive debugging

Depends on file-info (for fileType) and ffmpeg (for fileinfo/duration and the stream/{n} table). Runs on the background queue.