A content management system pre-transcodes portions of content items provided for storage. When a content item is uploaded to the content management system for storage, the content management system stores the content item in an original format. The content management system transcodes a portion of the content item from the original format to a streaming format. The content management system stores the transcoded portion and makes the content item available for access. When a client device requests the content item from the content management system, the content management system first sends by streaming to the client device the stored transcoded portion in the streaming format. During the sending of the transcoded portion, the content management system transcodes a remainder of the content item that has not been transcoded to the streaming format. The content management system sends the transcoded remainder of the content item to the client device.