pybag

A Python library to work with bag files (MCAP format) without ROS.

Warning

The library is still in the early stages of development and the API is still unstable

Installation

uv add pybag-sdk

Quick Start

# Get file information
pybag info data.mcap

# Filter messages
pybag filter data.mcap -o output.mcap --include-topic /camera

# Merge multiple files
pybag merge input1.mcap input2.mcap -o output.mcap

Reading MCAP Files

from pybag.mcap_reader import McapFileReader

with McapFileReader.from_file("data.mcap") as reader:
    for msg in reader.messages("/camera"):
        print(msg.log_time, msg.data)

Writing MCAP Files

from pybag.mcap_writer import McapFileWriter
from pybag.ros2.humble import std_msgs

with McapFileWriter.open("output.mcap") as writer:
    log_time_ns = 1000
    msg = std_msgs.String(data="hello")
    writer.write_message("/status", log_time_ns, msg)

Custom Messages

from dataclasses import dataclass
import pybag

@dataclass
class SensorData:
    __msg_name__ = 'custom/msg/SensorData'
    temperature: pybag.float32
    humidity: pybag.float32

with McapFileWriter.open("sensors.mcap") as writer:
    writer.write_message("/sensor", 1000, SensorData(25.5, 60.0))