According to some embodiments, a Single-InstructionMultiple-Data averaging instruction is used to process pixels of image data. The isolation sleeve may be an annular structure extending axially between the two annular axial end plates, and the isolation sleeve and the annular housing may define an isolation cavity therebetween. A headrest support frame is provided to the upper frame so as to be capable of moving in a front-and-back direction. Stream selection unit 17 selects a text subtitle stream judged as being able to be decoded.