In recent years, a multitude of innovative educational videos focusing on mathematics and employing dynamic visualization techniques have been published on YouTube. From a sample of videos, we develop a taxonomy of didactical roles of dynamic visuals and supporting animation techniques. The taxonomy is constructed through an open coding approach, involving an iterative process of defining, analysing and refining the codes. Additionally, we conducted an interview with a video creator about the intended roles of dynamic visuals employed in his animations. The taxonomy encompasses the following categories of roles: connect objects, (co)vary objects, dynamic concept visualization, dynamic process visualization, symbol sense, connect to reality and generalization. These roles are implemented through animation techniques like moving and morphing. The nomenclature of these roles suggests their affiliation with various mathematics education research perspectives, including covariational thinking, concept-process duality, symbol sense and conversion between registers. The taxonomy serves as a foundational framework for further research into the learning outcome and effectiveness of dynamic visualization in educational mathematics videos.