[1] https://obsproject.com/forum/resources/branch-output-streami...
The common case for the plugin is to do some preprocessing before importing the video into OBS, but you can also use the pipeline as a video filter, which is really powerful, because you can inject a filter into not only a single source, but also at any level of a nested scene. So you can scale/composite several inputs together and then the video filter can copy the source stream and encode/tee it to a file output. Might still be considered a hack of sorts.