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Jaguar CD CHD images

CHD is supported for Jaguar CD only when the file carries MAME's CHSE session-metadata tag (mamedev/mame#15886, merged 2026-08-15). That tag is the CHD equivalent of a CUE REM SESSION nn line.

Why most .chd files on the internet will not load

Jaguar CDs are two-session discs: session 1 is Red Book audio, session 2 is game data mastered as audio-type 2352-byte tracks. Classic chdman createcd flattened that into one session and dropped the ~11400-sector inter-session gap, so the TOC the BIOS and HLE walk is wrong.

Those files are refused at load with a [CD-CHD] error that points at issue #322 and tools/jagcd. Reconvert from a Redump CUE/BIN with jagcd-to-chd (or load a CDI directly). Do not try to "fix" an old CHD in place.

chdman 0.288 from Homebrew, and every CHD made before PR 15886, is in this class. chdman info on a good file shows a CHSE / SESSION:2 metadata blob; a bad file has only CHT2 track lines.

Convert

  1. Get the jagcd-tools-{linux-x64,macos,windows-x64}.zip from this repository's GitHub Releases (tagged v* and the rolling nightly). Each zip contains a chdman built from the commit in tools/jagcd/CHDMAN_PIN plus jagcd-to-chd and jagcd-chd-check. They ship next to the cores from release.yml.
  2. From a CUE:
./jagcd-to-chd "Game (USA).cue"

That runs chdman createcd and then jagcd-chd-check. Exit 0 is loadable. Exit 1 means the chdman you invoked is still too old — set JAGCD_CHDMAN to the binary from the zip, not the one on PATH.

createcd does not read .cdi. Use CUE/BIN as the source, or load the CDI directly in the core.

Virtual pregaps (exit 2 / log warning)

CHT2 PGTYPE values that start with V (e.g. VAUDIO) mean the pregap is silence, not stored audio. That is the same situation as a Redump CUE/BIN: HLE boot works (auth is bypassed), real-BIOS authentication may fail. The core warns and loads. CDI-class dumps that preserve INDEX 00 audio are the right source if you need BIOS-mode auth.

PR 15886 did not change pregap-byte encoding; it only added session tags.

Core behaviour

  • .chd is a path-loaded disc image, same as .cue / .cdi.
  • Missing CHSE on a Jaguar-shaped image (2+ all-audio tracks) → refuse.
  • CHSE present, virtual pregaps → warn, load.
  • CHD audio frames are stored as 16-bit PCM. The core byte-swaps them back to Jaguar I2S (CUE/BIN) order on read.
  • The ~11400-sector session gap is synthesized when CHSE shows a session change and the first session-2 track's PREGAP is not already that large (so a CHD that encoded the gap as a pregap is not double-counted). Measured on a post-15886 createcd of Frog Feast: every CHT2 PREGAP is 0 and PGTYPE is MODE1 (not virtual); extractcd emits a REM SESSION 02 that lands at the true session-2 track, matching the source CUE.
  • CHSE entries are indexed among themselves (search index 0 = the 1st CHSE entry in the file, 1 = the 2nd, ...), not by track position. Before issue #476 the CHD parser queried CHSE at the same search index as its track loop counter, which only happened to land on the right entry when session 1 has exactly one track — true for most retail Redump rips, but not for homebrew CUEs whose session 1 carries two or more tracks (Frog Feast, Ants, Klax, ...). That single-track assumption was the bug, not the CHD's own metadata: the parser now walks the whole metadata list in true on-disk order (CHDMETATAG_WILDCARD) and stamps each track with whichever session was current when it was encountered, so it agrees with extractcd's own placement regardless of how many tracks precede session 2.

The in-tree fixtures test/roms/synth_jagcd.chd (CHSE) and synth_jagcd_nosession.chd (pre-15886 / Homebrew 0.288 shape) were built with the pinned chdman using -c none so they stay tiny. CI and Homebrew 0.288 cannot recreate the CHSE file; that is why jagcd_roundtrip.sh exits 77 when the converter is missing. synth_jagcd_vpregap.chd adds three tracks with virtual (VAUDIO) pregaps, the layout Myst (USA) converts to, generated by test/tools/gen_synth_jagcd_vpregap.py (#774).

Tracking: issue #322.