A media source device includes media files in either original source format or in alternative digital formats, based on a content descriptor indicated by a client device from a plurality of content descriptors generated to represent possible transcodings of the source format. In the alternative, a media source device can receive a client device report and subsequent request for a media file. The media source device can send the media file to the client device in a particular digital format based on whether the content descriptor corresponding to the media file is compatible or incompatible with the client device. The bit rate used to send the media file to the client device can be adjusted based on the available transmit bit rate.