A variable-length data alignment apparatus receives header data (MHD) and blocks (B1-B6) from different sources, forms a header (MH) based on the received header data (MHD) and outputs the header (MH) followed by blocks (B1-B6). The variable-length data alignment apparatus has a RAM (4) for storing the header data (MHD), and a buffer (3) for storing the blocks (B1-B6). A processor (5) produces a plurality of commands (C1-C4) and processes the header data (MHD) from said first memory means (4). The commands are prosecuted in multiplexer (8) and bit stream coder (9) to form header (MH) and to append said blocks (B1-B6) from said first memory means (4) after said header (MH).