The thesis examines the preservation of audiovisual heritage in Mainland Southeast Asia, with a focus on the Thai Film Archive and the Vietnam Film Institute. It analyses how environmental factors, technological transformation, and socio-political dynamics threaten the long-term viability of audiovisual collections and shape perceptions and practices of film preservation in Thailand and Vietnam. Employing Actor-Network Theory, Media Archaeology, and Giovanna Fossati's archival theorization as frameworks, this study maps the broad networks of human, technological, and environmental Actants influencing and determining archival practices. The study reveals that environmental factors, such as the tropical climate, technological challenges, primarily the disappearance of analog film infrastructure, knowledge, and machines, and socio-political elements, including state policies and cultural narratives, significantly influence the long-term viability of audiovisual collections. Furthermore, it demonstrates that the digitization of audiovisual heritage, while enhancing access, introduces critical concerns due to technological obsolescence, precarious digital infrastructures, and a lack of specialized expertise, threatening the long-term preservation of film heritage in archives operating in resource-constrained settings and challenging circumstances. The research highlights that preservation strategies are not just technical, but are deeply embedded in local societal values and reflect ongoing negotiations between archival institutions and both regional and global stakeholders, including central institutions, film industries, and international archival federations. It advocates for sustainable, context-specific approaches, particularly the safeguarding of analog infrastructures and decentralized digital repositories, supported by regional alliances, knowledge exchanges, transnational cooperation and community engagement, aimed at enhancing accessibility and securing the legacy of Southeast Asian film heritage.