# Rosbag2 Recording > --- name: rosbag2-recording description: 'Record and play back ROS 2 bag files. Use when configuring rosbag2 recording, storage backends, or playback options.' --- # Role You are an expert in ROS 2 rosbag2 recording and playback. You guide correct bag recording, playback, storage format selection, and programmatic bag access in ROS 2 Jazzy/Rolling. ## Recording ```bash # Record all topics ros2 bag record -a # Record specific topics ros2 bag record /scan /odom /cmd_vel -o my_recording # Record with topic regex ros2 bag record --regex "/camera/.*" -o camera_data # Exclude topics ros2 bag record -a --exclude "/camera/image_raw|/pointcloud" # Record with compression (zstd) ros2 bag record -a --compression-mode file --compression-format zstd # Record with MCAP storage (recommended for Jazzy+) ros2 bag record -a -s mcap -o my_recording # Record with max bag size (split into multiple files) ros2 bag record -a --max-bag-size 1073741824 # 1 GB # Record with max duration ros2 bag record -a --max-bag-duration 300 # 5 minutes ``` ## Playback ```bash # Basic playback ros2 bag play my_recording # Publish clock for sim_time nodes ros2 bag play my_recording --clock # Playback at different speeds ros2 bag play my_recording --rate 2.0 # 2x speed ros2 bag play my_recording --rate 0.5 # half speed # Loop playback ros2 bag play my_recording --loop # Play specific topics only ros2 bag play my_recording --topics /scan /odom # Remap topics during playback ros2 bag play my_recording --remap /cmd_vel:=/robot/cmd_vel # Start from a specific time offset ros2 bag play my_recording --start-offset 30.0 # skip first 30s # Play until a specific duration ros2 bag play my_recording --playback-duration 60.0 # play 60 seconds # Pause/resume (press space in terminal) ros2 bag play my_recording --start-paused ``` ## Bag Information ```bash ros2 bag info my_recording # Output includes: # - Duration # - Start/end time # - Message count per topic # - Topic types # - Storage format (sqlite3/mcap) # - File sizes ``` ## Storage Backends ### SQLite3 (Default in Humble) - Single `.db3` file + `metadata.yaml` - Mature, widely supported - Slower for large bags, poor seek performance ### MCAP (Preferred for Jazzy/Rolling) - Single `.mcap` file - Much better read/write performance - Excellent seek performance (indexed) - Better compression support - Compatible with Foxglove Studio - Smaller file sizes ```bash # Set MCAP as default ros2 bag record -s mcap /scan /odom -o my_recording # Convert old SQLite3 bags to MCAP ros2 bag convert -i old_recording -o new_recording -s mcap ``` ## Python API for Reading Bags ```python from rosbag2_py import SequentialReader, StorageOptions, ConverterOptions from rclpy.serialization import deserialize_message from sensor_msgs.msg import LaserScan from rosidl_runtime_py.utilities import get_message def read_bag(bag_path): reader = SequentialReader() storage_options = StorageOptions(uri=bag_path, storage_id='mcap') converter_options = ConverterOptions( input_serialization_format='cdr', output_serialization_format='cdr') reader.open(storage_options, converter_options) # Get topic metadata topic_types = reader.get_all_topics_and_types() type_map = {t.name: t.type for t in topic_types} while reader.has_next(): topic, data, timestamp = reader.read_next() msg_type = get_message(type_map[topic]) msg = deserialize_message(data, msg_type) if topic == '/scan': print(f'[{timestamp}] Scan ranges: {len(msg.ranges)}') elif topic == '/odom': print(f'[{timestamp}] Odom x={msg.pose.pose.position.x:.2f}') ``` ## Python API for Writing Bags ```python from rosbag2_py import SequentialWriter, StorageOptions, ConverterOptions, TopicMetadata from rclpy.serialization import serialize_message from std_msgs.msg import String import time writer = SequentialWriter() storage_options = StorageOptions(uri='output_bag', storage_id='mcap') converter_options = ConverterOptions( input_serialization_format='cdr', output_serialization_format='cdr') writer.open(storage_options, converter_options) topic = TopicMetadata( name='/my_topic', type='std_msgs/msg/String', serialization_format='cdr') writer.create_topic(topic) msg = String() msg.data = 'hello' writer.write('/my_topic', serialize_message(msg), int(time.time() * 1e9)) ``` ## QoS Override During Playback ```yaml # qos_overrides.yaml /scan: reliability: best_effort durability: volatile /map: reliability: reliable durability: transient_local ``` ```bash ros2 bag play my_recording --qos-profile-overrides-path qos_overrides.yaml ``` ## Filtering by Time ```bash # Record with time trigger (start after delay) ros2 bag record -a --start-paused # Then resume via service: ros2 service call /rosbag2_recorder/resume ... # Programmatic time filtering during read while reader.has_next(): topic, data, timestamp = reader.read_next() time_sec = timestamp / 1e9 if time_sec < start_time or time_sec > end_time: continue # process message ``` ## Critical Warnings - **Disk space with cameras**: An uncompressed 1080p camera at 30fps generates ~1.5 GB/min. Always use compressed image topics (`/image/compressed`) or enable bag compression. PointCloud2 at 10Hz can exceed 500 MB/min. - **Clock for sim_time**: When playing back bags for nodes with `use_sim_time=true`, you MUST use `--clock`. Without it, nodes using sim_time will be stuck at time 0. - **Topic QoS mismatch on playback**: rosbag2 replays with the recorded QoS. If subscribers expect different QoS, use `--qos-profile-overrides-path`. - **MCAP for new projects**: Always use MCAP (`-s mcap`) for new recordings. SQLite3 is legacy and has poor performance for large bags. - **Bag corruption**: SQLite3 bags can corrupt on unclean shutdown. MCAP is more resilient. Always stop recording cleanly (Ctrl+C). - **Namespace changes**: If topics were recorded under a namespace (e.g., `/robot/scan`) but your nodes expect `/scan`, use `--remap` during playback. - **TF and playback**: TF transforms in the bag may conflict with a running robot. Use namespacing or topic remapping to avoid conflicts.