MCAP

An open-source multimodal logging file format from Foxglove, the default recording format for ROS 2 bags.

MCAP is an open-source container file format designed by the robotics software company Foxglove, used to store multiple timestamped data streams — camera images, point clouds, joint states, control commands, and so on — into a single file, organized by publish/subscribe channels. It's agnostic to serialization method, so ROS messages, Protobuf, JSON, and other formats can all be stored, and it writes each message's schema (structure definition) into the file itself, so the file stays readable even years after the code that wrote it has changed. It uses append-only writes, so data already written survives if a program crashes unexpectedly; it also supports chunked LZ4/Zstd compression and indexing for fast reads over a specific time range. Starting with ROS 2 Iron in May 2023, MCAP replaced SQLite as rosbag2's default storage format. Official read/write libraries exist for C++, Python, Go, Rust, Swift, and TypeScript. In embodied-AI data collection, it's commonly used as the raw recording format, later converted into training formats such as LeRobot or RLDS.

ExampleNVIDIA's Isaac Teleop framework uses MCAP to record and replay collected data, and can interoperate with the LeRobot dataset format; a recorded .mcap file can also be opened and played back directly in the Foxglove visualization tool.

Also called

.mcap

Related

ROS Bag · Robot Operating System 2 · Foxglove Studio · Hierarchical Data Format version 5 · LeRobotDataset · NVIDIA Isaac Teleop

Sources

MCAP 官网 (Chinese)
Foxglove: MCAP as the ROS 2 default bag format
ros2/rosbag2（GitHub）

As of

2026-09