feat: Add subscriber plugins using pluginlib

[Nosille]

Public API Changes

Reorganized codebase to isolate subscribers from streamers.
Make subscribers an additional pluginlib class (base_class_type="web_video_server::SubscriberFactoryInterface">)
Created image_transport and pointcloud2 subscribers

Description

This is a big change that will probably take a little back and forth. If you are not interested let me know. The goal was to make it possible to subscribe to ros msg formats other than images and convert them to image streams. This was done in a plugin-able fashion. Existing image_transport based subscription capabilities were removed from the existing streamer plugins and replaced with a new subscriber plugin. A new pointcloud2_subscriber plugin was added that subscribes to pointcloud2 msgs, projects them into a 2d image (user selected viewing frame with parameters for height, width, and focal length), then sends the resulting image to any of the existing streamers. A somewhat silly subscriber plugin example/tutorial was created in the docs that converts a string msg into an image.

[bjsowa]

Thank you for the PR. I'll try find some time to review it till the end of the week (ping me if I forget). My only request for now is to split it into 2 separate PRs, one that changes the classes structure and one that adds the pointcloud subscriber plugin.

[Nosille]

I finally found time to remove the pointcloud2 stuff. I will make a separate pull request after this one is complete.

[bjsowa]

Sorry I couldn't find much time to review this. I generally like the idea of separating streamers and subscribers. I quickly skimmed through the code and the solution looks alright. My only concern is that the subscriber interface only works for streamers which expect a raw image. This does not fit with the ros_compressed streamer which never decodes the image.

I'll try to take go back to it later next week. For now, try to pass CI.

[Nosille]

When I removed the pointcloud2 subscriber I didn't remove its dependencies. Most of these comments are a result of that. They have been removed now.

Seems like the CI/CD errors are all format related. I do not have much practice with formatters and my first attempt resulted in many more changes than I think you are looking for. Any advice? I don't see format guidance in this projects documentation.

The compressed image streamer is an odd ball that doesn't quite fit. I handled it by simply letting it stay the way it was , i.e., it doesn't actually use the subscriber list sent to it. Another weakness in my current implementation is that each streamer will use the first subscriber factory that says it can handle the current msg type. It currently isn't a problem, but could become one as redundant subscribers are added. I am a little unsure how best to handle it, and I am open to suggestions.

[bjsowa]

Seems like the CI/CD errors are all format related. I do not have much practice with formatters and my first attempt resulted in many more changes than I think you are looking for. Any advice? I don't see format guidance in this projects documentation.

For formatting, just use:

ament_uncrustify --reformat .

[bjsowa]

If you want to run clang-tidy tests locally, make sure to compile with -DCMAKE_EXPORT_COMPILE_COMMANDS=ON, for example:

colcon build --cmake-args -DCMAKE_EXPORT_COMPILE_COMMANDS=ON

then run:

ament_clang_tidy --packages-select web_video_server

If you want to make it faster, add --jobs flag, for example:

ament_clang_tidy --packages-select web_video_server --jobs 12

Some of the errors can be fixed automatically with --fix-errors flag

[bjsowa]

Hi @Nosille . Sorry for half a year of no response. Are you still down to work on this if I do a review?

[Nosille]

Yes. Sent via the Samsung Galaxy S25 Ultra, an AT&T 5G smartphone Get Outlook for Android<https://aka.ms/AAb9ysg>

…

________________________________ From: Błażej Sowa ***@***.***> Sent: Wednesday, 12 August 2026 16:41:51 To: RobotWebTools/web_video_server ***@***.***> Cc: Charles Ellison ***@***.***>; Mention ***@***.***> Subject: Re: [RobotWebTools/web_video_server] feat: Add subscriber plugins using pluginlib (PR #198) [https://avatars.githubusercontent.com/u/23124539?s=20&v=4]bjsowa left a comment (RobotWebTools/web_video_server#198)<#198 (comment)> Hi @Nosille<https://github.com/Nosille> . Sorry for half a year of no response. Are you still down to work on this if I do a review? — Reply to this email directly, view it on GitHub<#198?email_source=notifications&email_token=APSJGLTDVVVZHAV26BBCQJD5JTJA7A5CNFSNUABFM5UWIORPF5TWS5BNNB2WEL2JONZXKZKDN5WW2ZLOOQXTKMRXGI2TKOBQGA3KM4TFMFZW63VHNVSW45DJN5XKKZLWMVXHJLDGN5XXIZLSL5RWY2LDNM#issuecomment-5272558006>, or unsubscribe<https://github.com/notifications/unsubscribe-auth/APSJGLQZEJIJABUXTR4PED35JTJA7AVCNFSNUABEKJSXA33TNF2G64TZHMZDKNBYGAYDONZ3JFZXG5LFHMZTSMJXGEYTQMJYGSQXMAQ>. Triage notifications, keep track of coding agent tasks and review pull requests on the go with GitHub Mobile for iOS<https://github.com/notifications/mobile/ios/APSJGLXZWJPCQUN5LAODBR35JTJA7A5CNFSNUABFM5UWIORPF5TWS5BNNB2WEL2JONZXKZKDN5WW2ZLOOQXTKMRXGI2TKOBQGA3KM4TFMFZW63VHNVSW45DJN5XKKZLWMVXHJKTGN5XXIZLSL5UW64Y> and Android<https://github.com/notifications/mobile/android/APSJGLTR6PKGMSSAY7V6QBD5JTJA7A5CNFSNUABFM5UWIORPF5TWS5BNNB2WEL2JONZXKZKDN5WW2ZLOOQXTKMRXGI2TKOBQGA3KM4TFMFZW63VHNVSW45DJN5XKKZLWMVXHJLTGN5XXIZLSL5QW4ZDSN5UWI>. Download it today! You are receiving this because you were mentioned.Message ID: ***@***.***>

[bjsowa]

Apart from these changes, my small grit with this feature is that Subscriber abstraction assumes that all Streamers consume sensor_msgs/msg/Image messages which is not true for ros_compressed or any other streamer in the future that won't operate on raw images.

I'm ok with merging it as it is (apart from the few changes I requested) and then figure out a slightly improved abstractions later.

[bjsowa]

This tutorial was not updated for the interface changes.

[bjsowa]

Typo

Suggested change

	cv:putText(image, input_msg->data, cv::Point(30,250), cv::FONT_HERSHEY_SIMPLEX, 1.0, cv::Scalar(255, 0, 0), 2, cv::LINE_AA);
	cv::putText(image, input_msg->data, cv::Point(30,250), cv::FONT_HERSHEY_SIMPLEX, 1.0, cv::Scalar(255, 0, 0), 2, cv::LINE_AA);

[Nosille]

I'm ok with merging it as it is (apart from the few changes I requested) and then figure out a slightly improved abstractions later.

I think it would take little effort to swap from "sensor_msgs::msg::Image" to "cv_bridge::CvImage" if that works better for you. The underlying opencv data types could also be passed directly with a little more work. Such a changes is probably better done now than later given how fundamental the passed data type is.

If we go that route, I believe I can make the ros_compressed_streamer actually use the subscriber plugin.

[bjsowa]

I'm ok with merging it as it is (apart from the few changes I requested) and then figure out a slightly improved abstractions later.

I think it would take little effort to swap from "sensor_msgs::msg::Image" to "cv_bridge::CvImage" if that works better for you. The underlying opencv data types could also be passed directly with a little more work. Such a changes is probably better done now than later given how fundamental the passed data type is.

If we go that route, I believe I can make the ros_compressed_streamer actually use the subscriber plugin.

cv_bridge::CvImage still stores the raw image data whilst ros_compressed_streamer subscribe to compressed image and send it over TCP without decompressing the image.

[Nosille]

I'm ok with merging it as it is (apart from the few changes I requested) and then figure out a slightly improved abstractions later.

I think it would take little effort to swap from "sensor_msgs::msg::Image" to "cv_bridge::CvImage" if that works better for you. The underlying opencv data types could also be passed directly with a little more work. Such a changes is probably better done now than later given how fundamental the passed data type is.
If we go that route, I believe I can make the ros_compressed_streamer actually use the subscriber plugin.

cv_bridge::CvImage still stores the raw image data whilst ros_compressed_streamer subscribe to compressed image and send it over TCP without decompressing the image.

I see. Yea, that is different. It is effectively forwarding a raw data block.

[Nosille]

I still have the example files to work on, but everything else should be addressed.

[bjsowa]

There are some clang-tidy warnings: https://github.com/RobotWebTools/web_video_server/actions/runs/32172150041/job/95825587065?pr=198#step:3:1409

[bjsowa]

There's one clang-tidy warning left: https://github.com/RobotWebTools/web_video_server/actions/runs/32191528946/job/95886703206?pr=198#step:3:1375

Other than that, update the tutorials and we're good to go.

[Nosille]

Working on the example got me thinking more about what functions are virtual and what are not. Also moved the code to find a subscriber factory into the base streamer class.