Given the potentials of dialogic multimodal feedback (DMF) for L2 writing and the lack of research about students’ engagement with DMF, this study was conducted under the lens of Affordance Theory to explore how university students engage with the affordances (learning possibilities) of DMF for their L2 academic writing and the factors influencing their engagement with DMF (screencast feedback with dialogic features such as commenting or reacting). This case study took place in a class of 31 students studying an EMI course involving students’ L2 writing activities at a Vietnamese university. Three major data collection instruments included a student questionnaire, student in-depth interviews, and interaction logs with DMF. Findings reveal that students actively engaged with various affordances of DMF behaviorally, cognitively, agentively, and emotionally in different ways, such as rewatching, adjusting speed, and proactively interacting with DMF by asking questions. Emotional engagement is both a prominent form of engagement and a mediating factor, interacting with other engagement dimensions. Interestingly, though most students showed active perceived engagement with DMF, the interaction logs revealed certain dissimilarities in students’ actual engagement with DMF. Finally, cultural factors and learner differences are two potential factors influencing students’ engagement with DMF, especially in Vietnamese collectivist culture.