The ECM format allows you to reduce the size of a typical CD image file (BIN, CDI, NRG, CCD, or any other format that uses raw sectors; results may vary). It works by eliminating the Error Correction/Detection Codes (ECC/EDC) from each sector whenever possible. The encoder automatically adjusts to different sector types and automatically skips any headers it encounters. The results will vary depending on how much redundant ECC/EDC data is present. Note that for "cooked" ISO files, there will be no reduction.