Connector

MCAP

Replay MCAP recordings in any schema

Category

Robotics

Kind

source

Capabilities

StreamsHistoryEntities

Runs on

Linux x64Linux ARM64macOS Apple siliconmacOS IntelWindows x64

Replay an MCAP recording, the format Foxglove tools and the Foxglove SDK write. Its messages become Phloem channels and 3D scene geometry. Point it at one .mcap file or a folder of them; a folder plays in file-name order.

#What it reads

• Message encodings json, protobuf, cbor and msgpack, decoded from the schemas inside the file. Protobuf needs no generated code or .proto files. JSON needs no schema.
• Chunked or not, indexed or not, with zstd or lz4 compression.
• Unfinished files, such as when the robot lost power. Every message before the cut is read.
• Attachments and metadata records are listed when the replay starts. They are not stored yet.

Not read here:

• ROS topics (cdr or ros1 messages). Use the ROS 2 connector. These channels are skipped, named and counted.
• flatbuffer and capnproto messages. These are counted.

#What you get

• Scene — Foxglove's standard schemas draw in the 3D view, in the frame the message names: foxglove.PointCloud (any field type, with the cloud's own pose), LaserScan, FrameTransform and FrameTransforms (as TF edges), CompressedImage and RawImage. A cloud from the Foxglove SDK and one from a ROS topic share one scene.
• Scene, the rest — Foxglove poses, scene entities (arrows, cubes, spheres, cylinders, lines, triangles, text, models), grids, camera calibrations, location fixes (on the map) and image annotations draw in the 3D view and the camera view.
• Joints — foxglove.JointStates becomes one channel per joint, named by the robot: /joints/position/left_hip_pitch, /joints/effort/left_hip_pitch, with units (rad, rad/s, N·m, rad/s²). A limit can watch one joint; a chart can pick the joints it wants.
• Everything else — flattened to topic/nested/field channels. Numbers keep their type, text stays text. Byte fields, such as image pixels, are not channels. A message with nothing to plot still records a sample, so the topic is never silent.

#Setup

1. Browse to a recording. The table lists its topics: schema, encoding, message count, and what each becomes.
2. Tick the topics to bring in.
3. Choose Time (below) and Speed. Speed 0 loads as fast as the disk allows.

#Time

Choose message only when you trust the robot's clock.

Loop replays over and over, each pass timed from now.

#Missing data

If a channel's sequence counter jumps, the missing messages show as a gap on that channel. A counter that resets is a recorder restart, not a loss. At the end, a summary counts skipped channels, messages it could not decode, and messages read.

#Standards

• MCAP format: https://mcap.dev/spec · well-known registry: https://mcap.dev/spec/registry
• Foxglove schemas: https://docs.foxglove.dev/docs/visualization/message-schemas/introduction
• Tested against every reader test file the MCAP project publishes (416 files).

#Supports

• MCAP files and directories of them, chunked or not, indexed or not, zstd and lz4 chunks, files a crashed recorder never finished
• Message encodings json, protobuf, cbor, msgpack — decoded from the file's own schemas, no generated code
• Well-known robotics schemas: PointCloud, LaserScan, FrameTransform(s), CompressedImage, RawImage, JointStates, Log, SceneUpdate, Grid, CameraCalibration, LocationFix
• Sequence gaps stated as gap records per channel; attachments and metadata records listed

#Connection fields

Every field the Add input form shows for this connector.

Updated November 6, 2026