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CLI

The MCAP command line tool is useful for working with MCAP files.

Installation​

Release binaries​

Download binaries for your platform from the latest Github release.

Then, mark it executable:

$ chmod +x mcap

If required, move the binary onto your path.

Homebrew​

To install using Homebrew on macOS or Linux, run:

$ brew install mcap

From Source​

caution

Installing via go install is not supported. To build from source you must clone the repository.

  1. Clone the mcap repository.
  2. $ cd go/cli/mcap
  3. $ make build
  4. The binary will be built into the a newly created bin folder.

Usage​

Run mcap --help for detailed usage information.

$ mcap --help

Usage:
mcap [command]

Available Commands:
add         Add records to an existing MCAP file
cat         Cat the messages in an MCAP file to stdout
completion  Generate the autocompletion script for the specified shell
compress    Create a compressed copy of an MCAP file
convert     Convert a bag file to an MCAP file
decompress  Create an uncompressed copy of an MCAP file
doctor      Check an MCAP file structure
filter      Copy some filtered MCAP data to a new file
get         Get a record from an MCAP file
help        Help about any command
info        Report statistics about an MCAP file
list        List records of an MCAP file
merge       Merge a selection of MCAP files by record timestamp
recover     Recover data from a potentially corrupt MCAP file
version     Output version information

Flags:
    --config string   Config file (default is $HOME/.mcap.yaml)
-h, --help            help for mcap
-v, --verbose         Verbose output

Use "mcap [command] --help" for more information about a command.

ROS Bag to MCAP conversion​

Convert a ROS 1 bag file to mcap:

$ mcap convert demo.bag demo.mcap

Convert a ROS 2 db3 file to mcap:

$ mcap convert demo.db3 demo.mcap

In ROS 2 releases prior to Iron, db3 files did not contain message definitions (schemas). When converting to MCAP, you should first source the same ROS 2 workspace that the original file was recorded with. If this is not available, you will need to specify a search directory for message definitions (e.g /opt/ros/humble from the original system):

$ mcap convert demo.db3 demo.mcap --ament-prefix-path /path/to/humble

Alternatively, the ros2 bag convert utility may be used to convert between db3 and mcap.

File summarization​

Report summary statistics on an MCAP file:

$ mcap info demo.mcap
library: mcap go #(devel)
profile: ros1
messages: 1606
duration: 7.780758504s
start: 2017-03-21T19:26:20.103843113-07:00 (1490149580.103843113)
end: 2017-03-21T19:26:27.884601617-07:00 (1490149587.884601617)
compression:
    zstd: [14/14 chunks] (50.73%)
channels:
    (0) /diagnostics              52 msgs (6.68 Hz)    : diagnostic_msgs/DiagnosticArray [ros1msg]
    (1) /image_color/compressed  234 msgs (30.07 Hz)   : sensor_msgs/CompressedImage [ros1msg]
    (2) /tf                      774 msgs (99.48 Hz)   : tf2_msgs/TFMessage [ros1msg]
    (3) /radar/points            156 msgs (20.05 Hz)   : sensor_msgs/PointCloud2 [ros1msg]
    (4) /radar/range             156 msgs (20.05 Hz)   : sensor_msgs/Range [ros1msg]
    (5) /radar/tracks            156 msgs (20.05 Hz)   : radar_driver/RadarTracks [ros1msg]
    (6) /velodyne_points          78 msgs (10.02 Hz)   : sensor_msgs/PointCloud2 [ros1msg]
attachments: 0

Indexed reading​

Echo messages for a specific topic to stdout as JSON:

$ mcap cat demo.mcap --topics /tf --json | head -n 10
{"topic":"/tf","sequence":2,"log_time":1490149580.103843113,"publish_time":1490149580.103843113,"data":{"transforms":[{"header":{"seq":0,"stamp":1490149580.117017840,"frame_id":"base_link"},"child_frame_id":"radar","transform":{"translation":{"x":3.835,"y":0,"z":0},"rotation":{"x":0,"y":0,"z":0,"w":1}}}]}}
{"topic":"/tf","sequence":3,"log_time":1490149580.113944947,"publish_time":1490149580.113944947,"data":{"transforms":[{"header":{"seq":0,"stamp":1490149580.127078895,"frame_id":"base_link"},"child_frame_id":"radar","transform":{"translation":{"x":3.835,"y":0,"z":0},"rotation":{"x":0,"y":0,"z":0,"w":1}}}]}}
{"topic":"/tf","sequence":8,"log_time":1490149580.124028613,"publish_time":1490149580.124028613,"data":{"transforms":[{"header":{"seq":0,"stamp":1490149580.137141823,"frame_id":"base_link"},"child_frame_id":"radar","transform":{"translation":{"x":3.835,"y":0,"z":0},"rotation":{"x":0,"y":0,"z":0,"w":1}}}]}}
{"topic":"/tf","sequence":10,"log_time":1490149580.134219155,"publish_time":1490149580.134219155,"data":{"transforms":[{"header":{"seq":0,"stamp":1490149580.147199242,"frame_id":"base_link"},"child_frame_id":"radar","transform":{"translation":{"x":3.835,"y":0,"z":0},"rotation":{"x":0,"y":0,"z":0,"w":1}}}]}}
{"topic":"/tf","sequence":11,"log_time":1490149580.144292780,"publish_time":1490149580.144292780,"data":{"transforms":[{"header":{"seq":0,"stamp":1490149580.157286100,"frame_id":"base_link"},"child_frame_id":"radar","transform":{"translation":{"x":3.835,"y":0,"z":0},"rotation":{"x":0,"y":0,"z":0,"w":1}}}]}}
{"topic":"/tf","sequence":12,"log_time":1490149580.154895238,"publish_time":1490149580.154895238,"data":{"transforms":[{"header":{"seq":0,"stamp":1490149580.167376974,"frame_id":"base_link"},"child_frame_id":"radar","transform":{"translation":{"x":3.835,"y":0,"z":0},"rotation":{"x":0,"y":0,"z":0,"w":1}}}]}}
{"topic":"/tf","sequence":15,"log_time":1490149580.165152280,"publish_time":1490149580.165152280,"data":{"transforms":[{"header":{"seq":0,"stamp":1490149580.177463023,"frame_id":"base_link"},"child_frame_id":"radar","transform":{"translation":{"x":3.835,"y":0,"z":0},"rotation":{"x":0,"y":0,"z":0,"w":1}}}]}}
{"topic":"/tf","sequence":20,"log_time":1490149580.175192697,"publish_time":1490149580.175192697,"data":{"transforms":[{"header":{"seq":0,"stamp":1490149580.187523449,"frame_id":"base_link"},"child_frame_id":"radar","transform":{"translation":{"x":3.835,"y":0,"z":0},"rotation":{"x":0,"y":0,"z":0,"w":1}}}]}}
{"topic":"/tf","sequence":21,"log_time":1490149580.185428613,"publish_time":1490149580.185428613,"data":{"transforms":[{"header":{"seq":0,"stamp":1490149580.197612248,"frame_id":"base_link"},"child_frame_id":"radar","transform":{"translation":{"x":3.835,"y":0,"z":0},"rotation":{"x":0,"y":0,"z":0,"w":1}}}]}}
{"topic":"/tf","sequence":22,"log_time":1490149580.196638030,"publish_time":1490149580.196638030,"data":{"transforms":[{"header":{"seq":0,"stamp":1490149580.207699065,"frame_id":"base_link"},"child_frame_id":"radar","transform":{"translation":{"x":3.835,"y":0,"z":0},"rotation":{"x":0,"y":0,"z":0,"w":1}}}]}}

Remote file support​

All commands except convert support reading from remote files stored in GCS:

$ mcap info gs://your-remote-bucket/demo.mcap
library: mcap go #(devel)
profile: ros1
messages: 1606
duration: 7.780758504s
start: 2017-03-21T19:26:20.103843113-07:00 (1490149580.103843113)
end: 2017-03-21T19:26:27.884601617-07:00 (1490149587.884601617)
compression:
    zstd: [14/14 chunks] (50.73%)
channels:
    (0) /diagnostics              52 msgs (6.68 Hz)    : diagnostic_msgs/DiagnosticArray [ros1msg]
    (1) /image_color/compressed  234 msgs (30.07 Hz)   : sensor_msgs/CompressedImage [ros1msg]
    (2) /tf                      774 msgs (99.48 Hz)   : tf2_msgs/TFMessage [ros1msg]
    (3) /radar/points            156 msgs (20.05 Hz)   : sensor_msgs/PointCloud2 [ros1msg]
    (4) /radar/range             156 msgs (20.05 Hz)   : sensor_msgs/Range [ros1msg]
    (5) /radar/tracks            156 msgs (20.05 Hz)   : radar_driver/RadarTracks [ros1msg]
    (6) /velodyne_points          78 msgs (10.02 Hz)   : sensor_msgs/PointCloud2 [ros1msg]
attachments: 0

Remote reads will use the index at the end of the file to minimize latency and data transfer.

File Diagnostics​

List chunks in a file​

The mcap list command can be used with chunks or attachments:

$ mcap list chunks ~/data/mcap/demo.mcap
offset    length   start                end                  compression  compressed size  uncompressed size  compression ratio
43        4529455  1490149580103843113  1490149580608392239  zstd         4529402          9400437            0.481829
4531299   4751426  1490149580618484655  1490149581212757989  zstd         4751373          9621973            0.493804
9284910   4726518  1490149581222848447  1490149581811286531  zstd         4726465          9617327            0.491453
14013453  4734289  1490149581821378989  1490149582418243031  zstd         4734236          9624850            0.491876
18749879  4742989  1490149582428402906  1490149583010292990  zstd         4742936          9646234            0.491688
23494877  4712785  1490149583020377156  1490149583617657323  zstd         4712732          9619341            0.489923
28209799  4662983  1490149583627720990  1490149584217852199  zstd         4662930          9533042            0.489133
32874919  4643191  1490149584227924615  1490149584813214116  zstd         4643138          9499481            0.488778
37520119  4726655  1490149584823300282  1490149585411567366  zstd         4726602          9591399            0.492796
42248895  4748884  1490149585421596866  1490149586021460449  zstd         4748831          9621776            0.493550
46999820  4746828  1490149586031607908  1490149586617282658  zstd         4746775          9632302            0.492798
51748769  4759213  1490149586627453408  1490149587217501700  zstd         4759160          9634744            0.493958
56510103  4750731  1490149587227624742  1490149587814043200  zstd         4750678          9622778            0.493691
61262859  217330   1490149587824113700  1490149587884601617  zstd         217277           217255             1.000101