IGV 2.4 introduces support for sequence alignment data in CRAM 3.0 format. The specification can be found at

A corresponding index file is required. By convention, the index file name should be the same as the data file name, with “.crai” appended. For example, if the data file is named example_xyz.cram, the index file should be named example_xyz.cram.crai or example_xyz.crai.