An instantaneous decoder refresh, IDR, picture is encoded. The IDR picture occurs at a random access point in a bitstream of data, includes only intra-prediction slices, I-slices, and does not refer to any picture or pictures other than itself for prediction. When the IDR picture has a subsequent leading picture, a first Network Access Layer, NAL, unit type of the IDR picture is generated indicating that the IDR picture has a subsequent leading picture, and the first NAL unit type is encoded. When the IDR picture does not have a subsequent leading picture, a second Network Access Layer, NAL, unit type of the IDR picture is generated indicating that the IDR picture does not have a subsequent leading picture, the second NAL unit type being different from the first NAL unit type, and the second NAL unit type is encoded. The subsequent leading picture follows the IDR picture in the encoding order and precedes the IDR picture in a display order, and the subsequent leading picture is encoded without inter-prediction from any picture that precedes the IDR picture in the encoding order.