An audio encoding scheme or a stream that encodes audio and video data is disclosed. The scheme has particular application in mezzanine-level coding in digital television broadcasting. The scheme has a mean effective audio frame length F that equals the video frame length 1/fV over an integral number M video frames, by provision of audio frames variable in length F in a defined sequence where length = F(j) at encoding. The length of the audio frames may be varied by altering the length of overlap between adjacent frames in accordance with an algorithm that repeats after a sequence of M frames. An encoder and a decoder for such a scheme are also disclosed.