MCAP format for robot training data

Quick facts

Origin

Foxglove — MCAP container at mcap.dev, Apache-2.0 license; v1.0 specification published in 2022 as a successor to ROS bag for multi-language robotics logs.

Format design

Self-describing chunked binary; schema-aware; supports protobuf, ROS 1, ROS 2, JSON, FlatBuffer — 5 message-encoding ecosystems.

Compression

Built-in lz4 and zstd; per-chunk indexing for fast random reads (10x improvement over rosbag for partial-frame access).

Tooling

Foxglove Studio, mcap CLI, plus reader/writer libraries for Rust, Python, C++, Go, TypeScript (5 official SDKs).

Comparison

What is MCAP?

MCAP should be requested when the buyer's training or evaluation pipeline already expects time-synchronized robotics logs, compressed video topics, IMU, state, and action messages. Anchor the bounty to the canonical specification before suppliers submit samples ^[1], then use implementation documentation to make the expected file layout reviewable ^[2]. Robotics teams should also name the dataset or paper lineage they expect suppliers to support ^[3].

"MCAP is a modular container format and logging library for pub/sub messages with arbitrary message serialization."

For truelabel buyers, that quote matters because it turns MCAP robot data from a generic delivery preference into a source-backed requirement the supplier can test against a sample file.

Using MCAP with robot data

A useful MCAP sample should prove topic schema, timestamp domain, compression settings, camera topic, state topic, and manifest, plus file naming, manifest completeness, timestamp behavior, and rejected-example traceability. Include at least one workflow or converter reference so the supplier can show how the files load in practice ^[4], one interoperability reference for adjacent formats ^[5], and one comparison source for why this format is preferable to a raw folder dump ^[6].

Related pages

Use these to move from category-level context into specific task, dataset, format, and comparison detail.

External references and source context

1. MCAP specification

   MCAP is a container format for pub/sub message logs.

   MCAP ↩
2. MCAP guides

   MCAP guides document using MCAP with robotics data.

   MCAP ↩
3. Foxglove MCAP documentation

   Foxglove documents MCAP in visualization workflows.

   Foxglove ↩
4. rosbag2_storage_mcap

   rosbag2_storage_mcap connects MCAP to ROS 2 bag storage.

   GitHub ↩
5. ROS bag format 2.0

   ROS bag is the incumbent robot-native log format MCAP is often compared with.

   ROS Wiki ↩
6. ROS bag documentation

   ROS documentation explains recording bag files from robot nodes.

   docs.ros.org ↩

FAQ