Long block

See also Block switching

Audio encoding systems will commonly summarise the sound energy in one small stretch of time at a time. The duration of a single summarisation is also called a window and once a window of sound has been quantised, selected and packed, it can be considered as an individual block of audio information to be finaly stored in a frame.

Available mathematics used to summarise one block at a time can struggle with evenly representing details throughout a window's duration. There may be a tendency to mirror features at the start of the window onto the other end of the window, or the ends of the window might be the most efficient place to have details occur, it will depend on the particular mathematical transformation used. With such variance in transformation accuracy throughout each block, varying the size of blocks to best fit over the actual details present in the audio stream increases the overall accuracy of the encoding.

Lame has only two block sizes available, Long block and Short block. In Lame's case Short blocks require more data to describe less time than Long blocks so they are only selected when they significantly improve the alignment of transformation windows to audio details.