These are functional groups within the Alliance and often address one or more technical challenges. They are chaired by two member companies.
Sub-groups represent an idea within a working group that seems bigger than just a project (i.e., more than one challenge to address) but aren’t quite robust enough to warrant a separate working group. They usually have one chair.
Study groups are formed to investigate a particularly interesting aspect of the streaming video space (i.e., VR, AI, ML). That aspect is often too young of a technology to formalize specific responses such as a best practice, specification, or guideline.
Many of the working groups, sub groups, and study groups pursue projects related to the technical challenges in a variety of different topical areas.