An encoder comprising an input for inputting video signal to be encoded to form an encoded video signal comprising pictures of at least a first coded video sequence and a second coded video sequence, a hypothetical decoder for hypothetically decoding encoded video signal, an encoded picture buffer, and a decoded picture buffer, and a definer for defining a parameter indicative of the temporal difference between the last picture of the first coded video sequence and the first picture of the second coded video sequence in output/display order.