This study investigated the impact of extending video content into mixed reality (MR) environments on viewers’ immersive experiences. We proposed a particle-based spatial extension method, in which visual effects from within video content (e.g., snowstorms in “FROZEN”, flame portals in “AVENGERS ENDGAME”) are extended seamlessly into the surrounding space using MR head-mounted displays. This approach was compared with an existing character-based method, where related virtual objects were placed adjacent to the video frame. Experiments were conducted with Apple Vision Pro using Unity, involving both preliminary and main studies. Participants evaluated their experiences through a structured questionnaire assessing temporal perception, sense of presence, concentration, intrusiveness, and content congruence. Results showed that the particle-based method significantly enhanced presence, concentration, and congruence for both films, and improved temporal perception in “FROZEN”. These findings supported theories that surrounding, extensive visual information enhances immersion, and demonstrated that atmospheric visual effects can blur the boundary between video and environment more effectively than discrete object placement. The study offered theoretical contributions to understanding content-extension design in MR, and practical guidelines for creating next-generation entertainment experiences. Future work will explore longer viewing sessions, broader content types, and the integration of audio or haptic cues to further amplify immersion.