Features are provided for the asynchronous transmission of media files that are part of, or otherwise associated with, user-created content posts. The media file transmissions are asynchronous in nature because the media files are transmitted in parallel background processes while users continue creating content posts or performing other computing tasks. The client devices on which the media file transmissions are initiated can manage the establishment of connections to a network-accessible content management system, and also manage the continued transmission of the media files to the content management system while the users perform other tasks using the client devices.