Few algorithms do directly use data_index attributes
Few algorithms on the platform do directly use data_index{,_end} attributes of the inputs. The I/O uses the SynchronizationListener class to ensure that outputs are always synchronized with the main input channel. Therefore, the use of these attributes in the algorithm side should not be neither required nor allowed.
See the following issue for more details: https://gitlab.idiap.ch/biometric/beat.examples/issues/11