Streaming method and apparatus operating by inserting other content into main content

A method of reproducing media data, the method comprising:

• receiving a first file comprising information about period of a content, location information about a second file of external period and insertion information about the second file of the external period;
• receiving and reproducing at least one segment based on the received first file, wherein a plurality of media data, which is a set of encoded versions of the content, is presented during the period and the at least one segment is divided from one of the plurality of media data;
• receiving the second file based on the location information and insertion information;
• and
• receiving at least one external segment based on the second file,
• wherein the at least one external segment is divided from external media data of the external period, and
• wherein the location information indicates a location from which the second file is received and wherein the insertion information includes a forceplayout attribute indicating that the second file of the external period is accessed after a pre-determined event for referencing occurs.