Cause: Some CHDs include subchannel data (CD+G, EDC, ECC). A raw ISO discards this. Solution: Extract to BIN/CUE format, which preserves subchannel data:

chdman extractcd -i game.chd -o game.cue

This generates a .cue file and a .bin file. Use the .cue file with your emulator.

Cause: You modified the ISO but broke the file system structure or LBA (Logical Block Address) pointers. Solution: Use a dedicated CD image editor like CDmage (for PS1) or GDI Tools (for Dreamcast) to edit inside the ISO without extracting/remounting incorrectly.

This article explains how to convert CHD (Compressed Hunks of Data) files to ISO images for repacking or archival use. It covers what CHD is, why you might convert it, preparation steps, the conversion process (two common methods), and tips for repacking into a clean ISO.

After modification, you must create a new ISO. Do not just save over the original—build a fresh one.

Use:

Ensure you use the correct settings: Mode 1 (data) vs. Mode 2 (CD-i/Video CD), and include any necessary post-gap or ECC data.

mkdir /mnt/chd_iso
mount -o loop repacked_temp.iso /mnt/chd_iso
cp -a /mnt/chd_iso/* /tmp/repack_contents/
umount /mnt/chd_iso