Method of processing a bitstream by a decoder apparatus comprising: receiving by the decoder apparatus a bitstream, the bitstream comprising a plurality of bitstream parts, each bitstream part comprising encoded media data associated with a video tile, each video tile representing a different region in an output video frame, the encoded media data of a video tile configured for being independently decodable; the bitstream further comprising tile positioning information comprising tile identifiers and boundary identifiers, a tile identifier identifying encoded media data belonging to a video tile, the tile identifier being associated with one or more boundary identifiers, a boundary identifier identifying at least one boundary of the video tile identified by the tile identifier, the bitstream further comprising video tile size information; determining a tile map on the basis of the tile identifiers and the boundary identifiers, the tile map defining a spatial layout of video tiles, specifying the relative positions of the video tiles with respect to each other in the output video frame, the determining comprising determining that a first video tile and a second video tile have neighbouring boundaries on the basis of a boundary identifier of the first tile and a boundary identifier of the second tile; the first video tile and the second video tile having neighbouring boundaries if a predetermined relation between the boundary identifier of the first video tile and the boundary identifier of the second video tile exists; and, generating the output video frame on the basis of decoded media data of the video tiles and the tile map, wherein said generating comprises allocating a first buffer space in an output video frame buffer, said first buffer space configured for storing decoded media data of the first video tile, and allocating a second buffer space neighboring the first buffer space in the output video frame buffer for storing decoded media data of the second video tile, the size of the first buffer and second buffer space being determined on the basis of the video tile size information in the bitstream. receiving by the decoder apparatus a bitstream, the bitstream comprising a plurality of bitstream parts, each bitstream part comprising encoded media data associated with a video tile, each video tile representing a different region in an output video frame, the encoded media data of a video tile configured for being independently decodable; the bitstream further comprising tile positioning information comprising tile identifiers and boundary identifiers, a tile identifier identifying encoded media data belonging to a video tile, the tile identifier being associated with one or more boundary identifiers, a boundary identifier identifying at least one boundary of the video tile identified by the tile identifier, the bitstream further comprising video tile size information; determining a tile map on the basis of the tile identifiers and the boundary identifiers, the tile map defining a spatial layout of video tiles, specifying the relative positions of the video tiles with respect to each other in the output video frame, the determining comprising determining that a first video tile and a second video tile have neighbouring boundaries on the basis of a boundary identifier of the first tile and a boundary identifier of the second tile; the first video tile and the second video tile having neighbouring boundaries if a predetermined relation between the boundary identifier of the first video tile and the boundary identifier of the second video tile exists; and, generating the output video frame on the basis of decoded media data of the video tiles and the tile map, wherein said generating comprises allocating a first buffer space in an output video frame buffer, said first buffer space configured for storing decoded media data of the first video tile, and allocating a second buffer space neighboring the first buffer space in the output video frame buffer for storing decoded media data of the second video tile, the size of the first buffer and second buffer space being determined on the basis of the video tile size information in the bitstream.