A media file indexing service involves maintaining a media file index in a location external to the media file itself. The index is built up incrementally as the media file is being captured or transferred to shared storage. Client systems receive raw messages with information as to the location within the media file of media elements within each media file portion after it is written to shared storage, or receive refined messages indicating changes to the media file without the associated location information. Clients may query the index maintained by the index service for specific media elements during file capture, enabling edit-while-capture workflows.