Tools for the ffmpeg_image_transport

This repository hosts code for handling data streams produced by the ffmpeg_image_transport.

Supported systems

Continuous integration is tested under Ubuntu with the following ROS2 distros:

How to install

From packages

sudo apt-get install ros-${ROS_DISTRO}-ffmpeg-image-transport-tools

From source

Set the following shell variables:

repo=ffmpeg_image_transport_tools
url=https://github.com/ros-misc-utilities/${repo}.git

and follow the instructions here

Processing rosbags

Extract an mp4 file from a rosbag

The bag_to_file merges the ffmpeg-generated packets from a rosbag into a file:

bag_to_file -b input_bag -t topic -r rate [-o out_file] [-T timestamp_file] [-s start_time] [-e end_time]

The rate determines the fps used by ffmpeg when producing the output. The video is not transcoded, so what you get is the original stream, just in a mp4 container. To get correct playing speed the rate must match the rate at which the stream was originally recorded.

The start_time and end_time is given in seconds since the epoch, like the times you see when using ros2 bag info.

For example the following line produces a file video.mp4 and timestamps.txt from a rosbag:

ros2 run ffmpeg_image_transport_tools bag_to_file -t /cam1/image_raw/ffmpeg -r 40 -b ./my_rosbag/ -e 1710085164.466

The timestamp.txt file has the following entries:

# packet no, pts, header_stamp  recording_stamp
0 0 1710085154473057750 1710085156001866724
1 1 1710085155950467594 1710085156024209913

A H264 packet typically corresponds to a frame so the packet number conincides with the frame number.

Extract frames from a rosbag

The bag_to_frames decodes the ffmpeg-generated packets from a rosbag into frames:

bag_to_frames -b input_bag -t topic [-o out_dir] [-d decoder][-T timestamp_file] [-s start_time] [-e end_time]

The frames are written to out_dir with the ros header stamps embedded in the file name. A suitable decoder is usually guessed from the encoding used in the packet, but you can specify a valid ffmpeg decoder by using the -d decoder option. For start and stop times and the timestamp file see bag_to_file.

License

This software is issued under the Apache License Version 2.0.

Changelog for package ffmpeg_image_transport_tools

1.0.1 (2024-04-17)

• fix build issues on rolling
• Contributors: Bernd Pfrommer

1.0.0 (2024-04-15)

• initial release of ROS2 package
• Contributors: Bernd Pfrommer