extraction

Extraction & Track Information

CHDSharp can parse the CD/GD-ROM track layout stored in the metadata and extract the decompressed image to standard files.

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Classification

Chd.Classify returns the media type without decompressing:

var err = Chd.Classify("game.chd", out var kind);
// kind: "cd" | "dvd" | "hdd" | "gd-rom" | null (unknown)

The same logic is exposed per-instance via the IsCd, IsGdRom, IsDvd, and IsHdd properties.

Media	Detected by	Extraction output
CD-ROM	CHT2/CHTR/CHCD metadata	.bin + .cue
GD-ROM (Dreamcast)	CHGD/CHGT metadata	per-track .bin files + .gdi
DVD	DVD metadata	.iso
Hard disk	GDDD geometry (V1/V2: synthesized)	.img
Other (e.g. laserdisc A/V)	none of the above	.raw

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Track layout (TOC)

ChdFile.Tracks returns IReadOnlyList<ChdTrackInfo>? (null for non-disc images):

var err = ChdFile.Open("game.chd", out var chd);
using (chd)
{
    if (chd.Tracks is null)
    {
        Console.WriteLine("Not a CD/GD-ROM image");
        return;
    }

    foreach (var track in chd.Tracks)
    {
        Console.WriteLine(
            $"Track {track.TrackNumber}: {track.GetTypeString()} " +
            $"{track.Frames} frames @ {track.StartFrame}, " +
            $"pregap {track.PreGap}, postgap {track.PostGap}");
    }
}

The TOC parser (ChdTocParser) supports every metadata format, in priority order:

1. CHGT — GD-ROM (legacy) — also sets IsLittleEndianAudio
2. CHGD — GD-ROM (current)
3. CHT2 — CD tracks v2 (current, with pregap/postgap)
4. CHTR — CD tracks v1
5. CHCD — legacy binary track records (4-byte track count, 6×4-byte records per track, endianness auto-detected)

Tracks are padded to 4-frame alignment (ExtraFrames). GD-ROM images carry PadFrames.

Sector reads by LBA / MSF

Instead of raw byte offsets, CD/GD-ROM sectors can be read directly by logical block address (or BCD MSF):

using CHDSharp.Utils;

var sector = new byte[2352];                    // 2352-byte sector data
chd.ReadSector(0, sector);                      // LBA 0 = first track's INDEX 01
chd.ReadSectorMsf(0x00, 0x02, 0x00, sector);    // same sector, BCD MSF 00:02:00

var frame = new byte[chd.UnitBytes];            // full 2448-byte frame (data + subcode)
chd.ReadFrame(0, frame);

int lba = CdRomAddress.MsfToLba(0x02, 0x00, 0x00);   // 8850
var (m, s, f) = CdRomAddress.LbaToMsf(lba);           // (0x02, 0x00, 0x00)

LBA 0 maps to the first data track's INDEX 01: PreGap frames into the decompressed image when the pregap is stored physically (metadata PGTYPE:V..., e.g. CUE sheets with INDEX 00), and at image frame 0 otherwise (Redump-style CUEs, PREGAP-keyword CUEs, NRG, TOC, GDI). Non-CD/GD-ROM images return Chderrinvaliddata; out-of-range addresses or undersized buffers return Chderrinvalidparameter.

Legacy GD-ROM little-endian CDDA (CHGT / CD_FLAG_GDROMLE)

Legacy GD-ROMs detected via the CHGT tag store their CDDA audio tracks in little-endian byte order (Sega CD / PCEngine CD). ChdFile.IsLittleEndianAudio is true for these. To match MAME's playback behavior, ExtractToDirectory byte-swaps the 2352-byte sector-data portion of each 2448-byte frame only for AUDIO tracks when writing the per-track .bin files (subcode is left untouched). Raw Read() and hash/verification output are unchanged.

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Descriptor generation

CUE sheet (CD)

var cue = chd.GenerateCueSheet("game.bin");   // single-bin format
File.WriteAllText("game.cue", cue);

Example output:

FILE "game.bin" BINARY
  TRACK 01 MODE1/2048
    INDEX 01 00:00:00
  TRACK 02 AUDIO
    INDEX 01 01:00:00

GDI descriptor (GD-ROM)

var gdi = chd.GenerateGdiDescriptor(["track01.bin", "track02.bin", "track03.bin"]);

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Extraction

Simple variant

var created = chd.ExtractToDirectory("output", "game");
// returns the list of created files; throws InvalidDataException on failure

Reporting variant (no exceptions)

var result = chd.ExtractToDirectoryWithReporting("output", "game");
Console.WriteLine(result.Error.GetMessage());
foreach (var t in result.TrackResults)
    Console.WriteLine($"track {t.TrackNumber}: {(t.IsSuccess ? t.FilePath : t.Error.GetMessage())}");

Output mapping

Image type	Files written
CD	<base>.bin (whole disc, 2352-byte frames + subcode) + <base>.cue
GD-ROM	track01.bin … trackNN.bin (per track) + <base>.gdi
DVD	<base>.iso
HDD	<base>.img
Other	<base>.raw (raw decompressed image; e.g. laserdisc chav frames)

Extraction is sequential and streams hunk-by-hunk (WriteAllBytesSlow), so it works for images of any size without loading them into memory. Laserdisc A/V CHDs are not CD images — extractcd-style tools cannot convert them; CHDSharp extracts the raw A/V frame data (.raw), which is what chdman extractld consumes.

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TOC export

string toc = chd.ExportToc();   // human-readable table of contents
Console.WriteLine(toc);

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Notes

• Extraction requires a seekable stream and works on parent/child chains transparently (parent hunks are resolved through the parent instance).
• GenerateCueSheet/GenerateGdiDescriptor do not write the binary data — pass the actual output filenames so the descriptors reference them.
• Per-track extraction (TryWriteTrackToFile) uses UnitBytes for frame addressing; for CD images the unit size is the 2448-byte frame.