plugin-media

Host-side video transcoding for OpenCharly — the transcode: pipeline check verb, converting a captured MJPEG stream into an H.264 MP4 with the host's ffmpeg.

The plugin is an out-of-tree Go module: charly fetches this repo at the pinned tag, go-builds the provider on the host, and serves it out-of-process over go-plugin gRPC via the plugin SDK. The verb dispatches through the provider registry exactly like a built-in, executing in the evidence phase before venue teardown.

What it provides

Capability	Surface
verb:transcode	the transcode: pipeline verb — source MJPEG → H.264 MP4

The verb is host-side by construction: the MJPEG artifact a capture session flushes (e.g. spice: record) is already host-side, so the provider runs ffmpeg -y -loglevel error -i <mjpeg> -c:v libx264 -pix_fmt yuv420p <out> locally and writes the MP4 to the input's artifact (or the derived <source>.mp4 path). It self-evaluates the artifact validators and the shared exit_status/stdout/stderr matchers.

Requires host ffmpeg (with libx264 + yuv420p support).

How to use it

Compose the plugin candy in a box or check bed's candy: list, then use it in an instrument's pipeline::

instrument:
    - id: screen
      phase: [live]
      spice: {method: session, fps: 5}
      pipeline:
          - transcode: {to: mp4}          # map form
          - transcode: mp4                # scalar-sugar equal (primary field: to)

Field	Meaning
to	container format; only mp4 is supported (default)
artifact	host path the MP4 is written to; empty → derived from the source (<source>.mp4)
artifact_min_bytes	post-transcode artifact-size assertion
artifact_not_uniform	SOURCE-frame motion assertion, evaluated on the SOURCE MJPEG frames (pre-encode) — exact hashes of x264-encoded frames are vacuous (QP noise)

The shared matchers (exit_status/stdout/stderr) and timeout stay on core #Op and are self-evaluated by the provider against the ffmpeg run.

Layout

• candy/plugin-media/ — the plugin module: plugin.go (provider + meta registration), provider.go (the transcode verb provider), transcode.go, mjpeg.go, schema/transcode.cue (the self-contained #TranscodeInput), params/cue_types_gen.go, and cmd/serve/main.go.
• charly.yml — the root project manifest (discover: candy).
• .github/workflows/tag-on-merge.yml — CalVer tag + CHANGELOG/ on merge.

Related

• Owning skill: /charly-check:transcode — the transcode: capture-evidence pipeline verb reference (the plugin's user-facing surface; the candy carries its own transcode-skill: entity).
• /charly-check:check — the check verb catalog and plan-step surface the transcode: verb is authored through.
• /charly-internals:plugin — the plugin/provider model.
• opencharly/charly — the charly CLI.