ROS2 image transport for Foxglove CompressedVideo messages

This plugin provides a ROS2 image transport for encoding messages in Foxglove’s CompressedVideo message format, using the FFMpeg library. These messages can be recorded in a rosbag for processing with e.g. Foxglove Studio.

Encoding is based on the ffmpeg_encoder_decoder repo, which explains the compression process in more detail. Looking at the ffmpeg_image_transport documentation may also be helpful.

There is also an unsupported decoder provided for testing purposes. Use at your own peril.

Supported systems

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

Installation

From packages

sudo apt-get install ros-${ROS_DISTRO}-foxglove-compressed-video-transport

From source

Set the following shell variables:

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

and follow the instructions here

Make sure to source your workspace’s install/setup.bash afterwards. If all goes well you should see the transport show up:

ros2 run image_transport list_transports

should give output (among other transport plugins):

"image_transport/foxglove"
 - Provided by package: foxglove_compressed_video_transport
 - Publisher: 
      This plugin encodes frames into foxglove compressed video packets
    
 - Subscriber: 
      This plugin decodes frames from foxglove compressed video packets

Remember to install the plugin on both hosts, the one that is encoding and the one that is decoding (viewing).

Parameters

Publisher (camera driver)

Here is a list of the available encoding parameters:

• encoder: the libav (ffmpeg) encoder being used. The default is libx264, which is on-CPU unaccelerated encoding. Depending on your hardware, your encoding options may include the hardware accelerated h264_nvenc or h264_vaapi. You can list all available encoders with ffmpeg --codecs. In the h264 row, look for (encoders).
• preset: default is empty (“”). Valid values can be for instance slow, ll (low latency) etc. To find out what presets are available, run e.g. ffmpeg -hide_banner -f lavfi -i nullsrc -c:v libx264 -preset help -f mp4 - 2>&1 Note: deprecated, set parameter via encoder_av_options instead.
• profile: For instance baseline, main. See the ffmpeg website. Note: deprecated, set parameter via encoder_av_options instead.
• tune: See the ffmpeg website. The default is empty(“”). Note: deprecated, set parameter via encoder_av_options instead.
• gop_size: The number of frames between keyframes. For foxglove, this must be set to 1. The larger this number the more latency you will have, but also the more efficient the transmission becomes.
• bit_rate: The max bit rate [in bits/s] that the encoding will target. Default is ``8242880`.
• encoder_av_options: Set comma-separated list of libav encoder options with : as assignment operator, e.g. tune:<foo>,delay:<bar>.
• delay: Not sure what it does, but it doesn’t help with delay. Default is empty (“”). Note: deprecated, set parameter via encoder_av_options instead.
• pixel_format: Forces a different pixel format for internal conversions. See the ffmpeg encoder/decoder repo and the ffmpeg_image_transport repo for more.
• qmax: Max quantization rate. Defaults to 10. See ffmpeg documentation. The larger this number, the worse the image looks, and the more efficient the encoding.
• measure_performance: For performance debugging (developers only). Defaults to false.

The parameters are under the foxglove variable block. If you launch your publisher node (camera driver), you can give it a parameter list on the way like so:

``` parameters=[ params_path, { ‘image_raw.foxglove.encoder’: ‘h264_vaapi’, # ‘libx264’ ‘image_raw.foxglove.profile’: ‘main’, ‘image_raw.foxglove.preset’: ‘ll’,

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