bag_to_video_pkg

Description

The bag_to_video_pkg is a ROS (Robot Operating System) package designed to convert camera data from a ROS bag file into a video file. A ROS bag is a file format in ROS for storing ROS message data. These bags are primarily used for logging sensor data and messages transmitted over ROS topics and are very useful for capturing a snapshot of the system's state for later analysis and visualization.

This package specifically listens to a camera topic within a ROS bag file and saves the image data as a video file. It's useful for situations where you need to extract and view camera footage from a robotic system for analysis or record-keeping.

Prerequisites

• ROS Melodic (or compatible version)
• Python 2.7
• OpenCV
• cv_bridge

Installation and Building

1. Navigate to your ROS workspace (e.g., ~/catkin_ws/src).
2. Clone or copy the bag_to_video_pkg into the src directory.
3. Navigate back to the root of your workspace (e.g., ~/catkin_ws) and run catkin_make or catkin build depending on how you iniralized your catkin_ws.
4. Source the environment: source devel/setup.bash.

Running the Package

1. To launch the package, use the following command:

   roslaunch bag_to_video_pkg bag_to_video.launch

2. In a separaete terminal, play the ROS bag file you want to process:

   rosbag play <path_to_your_bag_file.bag>

3. A new window will pop open and you can visualize the ros bag contents at the same time
4. To verify everything is working and the images are being converted you can run the following command in a new window and visualize the ros logs of the script.

   rostopic echo /rosout
   
   

Ensure that the ROS environment is sourced in this terminal as well.

Topics

The package subscribes to the following topic to receive camera data:

• /camera/color/image_raw: This topic is expected to provide images from the camera in a raw format.

Output

• The script saves the output video in the root directory of the package as output.avi. You can modify the script to change the format, filename, or saving directory.

Customization

To customize the package for different topics or different video settings, edit the bag_to_video.py script located in the scripts directory of the package. Modify where you would like the output_directory variable point at.

Ubuntu Video Editors

Kdenlive for Editing ROS Bag Videos

After converting ROS bag files to video format using the bag_to_video_pkg, you might need to edit these videos for various purposes, such as trimming unnecessary footage or highlighting specific segments. For Ubuntu users, a highly recommended video editing tool is Kdenlive.

Why Kdenlive?

• Compatibility: Kdenlive is well-suited for Ubuntu and integrates seamlessly with its desktop environment.
• Features: It offers a wide range of editing features which are perfect for handling videos converted from ROS bag files.
• Ease of Use: Kdenlive has a user-friendly interface that is suitable for both beginners and professional editors.

Installing Kdenlive

1. Kdenlive can be easily installed from the Ubuntu Software Store. Follow these steps:
2. Open the Ubuntu Software Store. Search for "Kdenlive".
3. Click on the Kdenlive application and press "Install".

Editing ROS Bag Videos

Once you have Kdenlive installed, you can use it to edit the videos created by the bag_to_video_pkg. This can be particularly useful for:

• Removing unnecessary footage from the video.
• Enhancing video quality by adjusting color, contrast, and brightness.

Steps to Edit Videos

1. Launch Kdenlive.
2. Import your converted video file (now in MP4 format) into Kdenlive.
3. Use Kdenlive's timeline and tools to trim or adjust the video as needed.
4. Export the edited video in your desired format. Click this link for an mp4 format.

Next Steps?

If you want to create a custom dataset from the mp4 video you created and need to take many screenshots, check out this repository, which automates screenshot-taking.