There is provided a method comprising encoding an uncompressed constituent frame into a first encoded picture, said encoding also resulting into a reconstructed first picture and said constituent frame having an effective picture area within the first reconstructed picture, performing either of the following as a part of said encoding: inserting at least one sample value outside the effective picture area to form a boundary extension for the constituent frame in the reconstructed first picture; or saturating or wrapping oversample locations outside the effective picture area to be within the effective picture area. There is also provided a method comprising receiving an encoded picture, decoding the encoded picture to form a reconstructed constituent frame of the picture having an effective picture area; and performing either of the following: filling an area outside the effective picture area to produce a padded reference picture, wherein the filled area forms a boundary extension; or determining that when referring to sample locations outside the effective picture area in decoding, said sample locations are saturated or wrapped over to be within the effective picture area.