The present disclosure relates to a content supply device, a content supply method, a program, and a content supply system, which are capable of extending the DASH and seamlessly switching reception and reproduction of unicast transmission, multicast transmission, or broadcast transmission. A content supply device includes a HTTP transmitting unit that unicast-transmits a segment file of streaming data according to HTTP, an RTP transmitting unit that stores the segment file in an RTP packet without change, and transmits the RTP packet through at least one of multicasting and broadcasting according to RTP, and a metafile generating unit that generates a metafile in which a temporal correspondence relation between the segment file transmitted according to the HTTP and the segment file transmitted according to the RTP is described, and supplies the metafile to a reception side. The present disclosure can be applied to a system that delivers content in a streaming manner.