The time frame over which samples are blocked depends to some extent on the nature of the signal. It is inefficient to block on too short a time scale as this incurs an overhead in the computation and transmission of the prediction parameters. It is also inefficient to use a time scale over which the signal characteristics change appreciably as this will result in a poorer model of the signal. However, in the implementation described below the linear predictor parameters typically take much less information to transmit than the residual signal so the choice of window length is not critical. The default value in the shorten implementation is 256 which results in 16ms frames for a signal sampled at 16 kHz.
Sample interleaved signals are handelled by treating each data stream as independent. Even in cases where there is a known correlation between the streams, such as in stereo audio, the within-channel correlations are often significantly greater than the cross-channel correlations so for lossless or near-lossless coding the exploitation of this additional correlation only results in small additional gains.
A rectangular window is used in preference to any tapering window as the aim is to model just those samples within the block, not the spectral characteristics of the segment surrounding the block. The window length is longer than the block size by the prediction order, which is typically three samples.