PREPROCESSING
PREPROCESSING references a method that does things before a layer is decoded. Such a preprocessor has access to the layer data (as transformed by the FRAME_BEFORE_DECODING method if there is one), uninitialized field values (ai64Field), and inter-frame data. Note that a PreProcessing method cannot make any changes to the frame; that is the province of the FRAME_BEFORE_DECODING method. You can have multiple PreProcessing invocations in a decoder. For example:
PREPROCESSING (DoThat)