An encoding system may include a metadata manager, a key manager, and an encoder. The metadata manager may interface with one or more metadata sources to determine whether to include a metadata item from the one or more metadata sources. The key manager may determine whether the metadata item can be represented using one of already-allocated keys or an inline key must be used to represent the metadata item. The encoder may encode the metadata. If an inline key must be used to represent the metadata item, the encoder may associate the inline key and the type of the metadata item to the media file, and the encoder may encode the metadata item using the inline key in the media file.