AU is a document format: it stores data in the AU format. MP4 is a video format that packages H.264 or H.265 video with AAC audio in a container format widely supported across every platform and device. This conversion changes the file's encoding, compression method, and supported feature set. Metadata such as creation date and embedded colour profiles is preserved where the target format supports it. Converting between these two formats is common when the source application does not support MP4 natively or when the target platform only accepts MP4. 1converter processes this conversion server-side using open-source tools. Files are transferred over HTTPS, converted on secure cloud servers, and automatically deleted after 24 hours.