Compounds of formula :wherein R1 is C1-6alkylamino, C1-6alkoxy, or C3-7cycloalkyloxy; m is an integer having a value of 3 to 6; n is an integer having a value of 0 to 4; and salts thereof are inducers of human interferon. The first pivoting element is fixed to a base, and has a first internal space and an opening exposing the first internal space. If the video data stream precedes the audio data stream, the video data stream is delayed by an integer number of video frames and the audio data stream is delayed by an integer number of audio sample periods.