Won't play parallel bags in two different folders

[michael-code19]

Description

I have multi-file bag files in two folders, /folder1/folder1_sub/ and /folder2/folder2_sub/. I want to play back both the folders at the same time. Using the folder directory ros2 bag play folder1/folder1_sub folder2/folder2_sub does not play the bag files in parallel.

EX I want this to work:

ros2 bag play LIDAR_TOPICS/LIDAR_TOPICS OTHER_TOPICS/other_topics

Expected Behavior

I expect ros2 bag play to open both folders and play the bags in parallel

Actual Behavior

usage: ros2 [-h] [--use-python-default-buffering] Call ros2 <command> -h for more detailed usage. ... ros2: error: unrecognized arguments: OTHER_TOPICS/other_topics

To Reproduce

** Steps to reproduce the behavior, e.g.

1. Create two multi-file bag files and put them in folder1/folder1_sub/ and folder2/folder2_sub
2. Attempt to play them back in parallel using ros2 bag play folder1/folder1_sub/ and folder2/folder2_sub
3. You will get error

System (please complete the following information)

• OS: Ubuntu
• ROS 2 Distro: Humble
• Install Method: APT
• Version: 0.15.9

Additional context

Add any other context about the problem here

[fujitatomoya]

how about merging bag files into one via ros2 bag convert -i xxx -i yyy -o zzz.yaml and the use it with ros2 bag play zzz? see more details for https://github.com/ros2/rosbag2?tab=readme-ov-file#converting-bags

[MichaelOrlov]

@michael-code19

Using the folder directory ros2 bag play folder1/folder1_sub folder2/folder2_sub does not play the bag files in parallel. EX I want this to work: ros2 bag play LIDAR_TOPICS/LIDAR_TOPICS OTHER_TOPICS/other_topics

To accomplish your wants, you need to understand that someone behind the scenes should run multiple instances of the rosbag2 player for each bag file which is supposed to be playing in parallel. If we do so, then someone could complain that he wants or expects to be able to provide different filters or other configurations for each played bag file or complain that one bag started playing a few milliseconds earlier than the other or the player runs out of memory or CPU resources or something else. We don't want to mess up and we will not go this way!!! The current behavior is a WAD (Works As Designed). However, we allow one to do it themselves. In the world of recording and playback, this feature names distributed recording or playback. If one wants to playback multiple bags in parallel simultaneously, he can start multiple instances of the player in pause mode first. i.e., start each player instance in a separate terminal window or process with the CLI option --start-paused. Then resume playback on all instances via one service call

ros2 service call rosbag2_player/resume rosbag2_interfaces/Resume

[MichaelOrlov]

• Closing since this is not a bug and rosbag2 works as designed.

[danil-tolkachev]

this is not a bug and rosbag2 works as designed

@MichaelOrlov sorry to hear that. In ROS1 I was able to play multiple bag-files at the same time.