Implementation:CARLA simulator Carla Client Start Recorder

Knowledge Sources	CARLA Simulator CARLA Documentation
Domains	Simulation, Recording
Last Updated	2026-02-15 00:00 GMT

Overview

Concrete tool for initiating simulation recording to a binary log file provided by the CARLA simulator.

Description

The Client.start_recorder method instructs the CARLA server to begin capturing all simulation state changes into a binary recording file. Once called, every subsequent simulation tick is logged until stop_recorder is invoked. The method accepts a filename for the output recording and an optional flag to capture additional data such as vehicle light states and bounding box information.

The filename can be an absolute path or a relative filename. When a relative filename is provided, the recording file is saved in the default CARLA recording directory on the server (typically CarlaUE4/Saved/ on the server machine). The method returns a string confirming the recording has started and the path where the file will be written.

If additional_data is set to True, the recorder captures extra per-frame information including vehicle light states, bounding boxes, and kinematics. This increases the file size but provides richer data for post-recording analysis and is required for certain inspection queries.

Usage

Call this method before running any simulation scenario that you want to capture. It should be invoked after connecting to the CARLA server and loading the desired map, but before spawning actors or beginning the simulation loop. The recorder will capture all subsequent events including actor spawns, so starting it early ensures complete coverage.

Code Reference

Source Location

• Repository: CARLA
• File: PythonAPI/carla/src/Client.cpp:L204, LibCarla/source/carla/client/Client.h:L121-123

Signature

Client.start_recorder(filename: str, additional_data: bool = False) -> str

Import

import carla

I/O Contract

Inputs

Name	Type	Required	Description
filename	str	Yes	Path or name of the binary recording file to create. If relative, saved to the server's default recording directory.
additional_data	bool	No	When True, records additional per-frame data including vehicle light states, bounding boxes, and kinematics. Defaults to False.

Outputs

Name	Type	Description
return	str	Confirmation string indicating recording has started and the resolved file path on the server.

Usage Examples

Basic Example

import carla

# Connect to CARLA server
client = carla.Client('localhost', 2000)
client.set_timeout(10.0)

# Load desired map
world = client.load_world('Town03')

# Start recording with a simple filename
result = client.start_recorder("recording_town03_session01.log")
print(result)  # Prints confirmation and file path

# ... run simulation scenario ...

# Stop recording when done
client.stop_recorder()

Advanced Example with Additional Data

import carla
import datetime

client = carla.Client('localhost', 2000)
client.set_timeout(10.0)

world = client.load_world('Town05')

# Generate a timestamped filename for organized recording storage
timestamp = datetime.datetime.now().strftime("%Y%m%d_%H%M%S")
filename = f"/home/carla/recordings/Town05_{timestamp}.log"

# Start recording with additional data enabled for richer analysis
result = client.start_recorder(filename, additional_data=True)
print(f"Recording started: {result}")

# Configure synchronous mode for deterministic recording
settings = world.get_settings()
settings.synchronous_mode = True
settings.fixed_delta_seconds = 0.05
world.apply_settings(settings)

# Spawn vehicles and run scenario
blueprint_library = world.get_blueprint_library()
spawn_points = world.get_map().get_spawn_points()

vehicles = []
for i in range(20):
    bp = blueprint_library.filter('vehicle.*')[i % len(blueprint_library.filter('vehicle.*'))]
    vehicle = world.try_spawn_actor(bp, spawn_points[i])
    if vehicle is not None:
        vehicle.set_autopilot(True)
        vehicles.append(vehicle)

# Run simulation for 500 ticks
for _ in range(500):
    world.tick()

# Cleanup
client.stop_recorder()
for v in vehicles:
    v.destroy()

Related Pages

Implements Principle

• Principle:CARLA_simulator_Carla_Simulation_Recording