MCAP Slice for VS Code

MCAP Slice opens indexed .mcap recordings directly inside desktop VS Code. The source recording stays on the workspace host and is always treated as read-only.

Features

• Inspect recording bounds, profile, library, topics, channels, schemas, and message counts.
• Select a millisecond-precision [In, Out) range with RFC 3339 timestamps displayed in Asia/Shanghai.
• Select topic names for export. All channels with the same selected topic name are preserved.
• Preview individual JPEG or PNG frames from ROS 2 CDR sensor_msgs/msg/CompressedImage channels without loading image payloads into the timeline.
• Load a local URDF and preview ROS 2 CDR sensor_msgs/msg/JointState at the same MCAP log_time cursor as the video and range controls.
• Keep video and robot previews side by side at every editor width. The export workspace prioritizes the frequently used range and Export action, while Topics, compression, and recording details use a compact disclosure sidebar. Drag its divider when long topic names need more room; arrow keys resize the focused divider and a double-click restores its default width.
• Derive interactive highlights, range controls, progress, and the robot stage grid from the active VS Code theme accent instead of fixed bright colors.
• Remember export topics, video topic, JointState topic, and URDF per workspace; topic-name matching lets the choices carry across MCAP files even when channel IDs differ.
• Resolve URDF meshes from relative paths, package://, or approved HTTPS origins. STL, GLB, DAE, OBJ/MTL, and glTF external dependencies are bundled by the extension host before the Webview loads them.
• Reuse prepared robot bundles across MCAP editor sessions. HTTPS bundles open from local cache for 24 hours before conditional revalidation; changed local mesh dependencies invalidate their bundle immediately.
• Export indexed slices with Zstandard, LZ4, or no compression.
• Preserve schemas, selected channels and their metadata, and top-level MCAP Metadata, then append mcap_slice.provenance.v1.

Usage

1. Install the VSIX and open a file with a .mcap extension from the Explorer.
2. Optionally select Load URDF…, choose a local .urdf, and select a compatible JointState topic. The workspace restores these preview choices when another MCAP is opened.
3. Choose the In and Out timestamps and explicitly select at least one topic. If needed, drag the divider beside Topics to reveal longer names.
4. Choose a compression mode and select Export Slice….

MCAP Slice writes a uniquely named temporary file beside the destination and only replaces the destination after the writer closes successfully. It refuses to use the source recording as the destination. If the source size or modified time changes, export is disabled until Reload Source is selected.

Workspace support

The extension runs as a workspace extension and supports desktop VS Code with:

• local folders;
• Remote - SSH;
• WSL; and
• Dev Containers.

For remote workspaces, reading and export happen on the remote workspace host. URDF files and local meshes are also read there, and approved HTTPS robot assets are downloaded and cached by that extension host. MCAP sources must be file: resources with random file access. The extension does not run in vscode.dev, virtual workspaces, or browser extension hosts.

Current limitations

• The MCAP must contain a usable Summary and Chunk Index. The extension does not fall back to a full sequential scan.
• Attachments are reported but are not copied to exported recordings.
• Video is single-stream, frame-by-frame preview only. There is no playback, multi-stream synchronization, or depth-image preview.
• Robot state decoding supports ROS 2 CDR sensor_msgs/msg/JointState only. Each message is treated as a complete snapshot; partial updates are not accumulated between messages.
• Robot input is a local .urdf; Xacro, MJCF, joint editing, and continuous robot playback are not supported.
• Frame indexes, JointState indexes, range bounds, compression, and source contents are not persisted after the editor tab closes. Export topic names, video and JointState topic names, the last URDF, and persistent HTTPS-origin approvals are remembered per workspace. A missing remembered topic causes a temporary fallback for that MCAP without replacing the saved preference.

The extension sends no telemetry. It contacts an HTTPS origin only when a URDF references it and the user explicitly allows that origin for the current load or workspace. Downloads run in the extension host without cookies or credentials; the Webview cannot connect directly to arbitrary HTTPS services. It otherwise uses a restrictive Content Security Policy and VS Code theme variables.

Use MCAP Slice: Clear Robot Asset Cache to force the next remembered URDF load to rebuild its bundle and revalidate or download HTTPS assets.

Development

Requires Node.js 22 and VS Code 1.95 or newer.

cd vscode-extension
npm ci
npm run typecheck
npm run lint
npm test
npm run test:integration
npm run package

The VSIX is written to ../dist/mcap-slice-vscode.vsix. Integration tests download an isolated VS Code runtime into the ignored .vscode-test/ directory.

Release candidates should also follow the manual smoke matrix.

Marketplace releases

Release packaging is driven by version tags. CI does not receive Marketplace credentials and never publishes automatically.

For each release, update the version in both package.json and package-lock.json, update this extension changelog, and merge those changes to main. Then create and push the matching tag:

extension_version="$(node -p "require('./vscode-extension/package.json').version")"
git tag "vscode-v${extension_version}"
git push origin "vscode-v${extension_version}"

The tag must exactly match vscode-vX.Y.Z. The package workflow installs from the lock file, runs typecheck, lint, unit/worker tests, the isolated VS Code integration test, packages one VSIX, and uploads it as the mcap-slice-vscode-X.Y.Z workflow artifact.

After the workflow succeeds, download and extract that artifact from Actions → Package VS Code Extension. In the Visual Studio Marketplace publisher portal, choose New extension → Visual Studio Code and upload the contained mcap-slice-vscode.vsix. The matching publisher and extension ID make it a new version of the existing listing. Marketplace versions cannot be overwritten, so always increment the extension version before creating another release tag.

License

MCAP Slice is available under the MIT License. Third-party notices are documented in the repository's Third-party notices.