encoder

CHD creation (CHDSharpEncoder)

CHDSharpEncoder is the encoder companion to the CHDSharp reader. It writes CHD v5 files from raw binaries and CD images (CUE/GDI/ISO/TOC), re-compresses existing CHDs (Copy), creates differential (delta) children against a parent, and writes uncompressed CHDs (-c none) — producing files that are byte-for-byte identical to chdman when the same codec is used, pass chdman verify, and extract back identically via chdman extractraw.

Full API docs and project layout: CHDSharpEncoder/README.md. Implementation plan and validation history: References/EncoderPlan.md.

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Capabilities

Raw encode	ChdEncoder.EncodeRaw(source, chdPath, hunkBytes, unitBytes, codecTags, options)
CD encode	ChdEncoder.EncodeCd(cuePath, chdPath, hunkBytes, unitBytes, codecTags, options)
Copy / re-compress	ChdEncoder.Copy(sourceChd, chdPath, codecTags, options) — any V1–V5 source, metadata cloned
Input formats	raw binary; CUE/BIN, GDI, ISO, TOC (cdrdao-style); existing CHD files
Codecs	zlib (default), zstd, lzma, huff, flac, cdzl, cdlz, cdzs, cdfl, none — up to 4 per file, smallest output per hunk
Deduplication	SELF references (CRC/SHA-1 keyed), with SELF_0/SELF_1 map promotion
Delta (parent) CHDs	ChdEncodeOptions.ParentPath — COMPRESSION_PARENT refs, unit-split windows, chdman -op parity
Uncompressed CHD	-c none — V5 raw map, hunk-aligned raw data, zero hunks skipped, chdman byte-identical
Metadata	CHT2 (CD), CHGD (GD-ROM), GDDD (HDD), DVD entries, checksummed, combined SHA-1
CD audio	byte-swapped to big-endian (as stored on disc), tracks padded to 4-frame boundaries
Ratio logging	per-hunk callback (ChdEncodeOptions.HunkCompleted) — never changes output

using CHDSharpEncoder;

ChdEncoder.EncodeRaw("game.bin", "game.chd");                       // raw, zlib
ChdEncoder.EncodeCd("game.cue", "game.chd");                        // CD, zlib
ChdEncoder.EncodeRaw("game.bin", "game.chd", 65536, 4096,
    ChdCodecs.ParseCodecTags("zlib,zstd,lzma"),
    new ChdEncodeOptions { HunkCompleted = p => Console.WriteLine(
        $"hunk {p.HunkIndex}/{p.HunkCount} {p.CodecName} {p.Ratio:P1}") });
ChdEncoder.Copy("old.chd", "new.chd", codecTags: [CodecTags.Zstd]); // re-compress
ChdEncoder.EncodeRaw("game.bin", "game.chd", 4096, 512,
    options: new ChdEncodeOptions { ParentPath = "base.chd" });     // delta child
ChdEncoder.EncodeRaw("game.bin", "game.chd", codecTags: [CodecTags.None]); // uncompressed

Callbacks fire in hunk order and are purely observational — encoding with a callback produces byte-identical output to encoding without one.

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Validation

The encoder is validated against chdman.exe v0.288 and the CHDSharpLib reader (350 tests in CHDSharpEncoderTest):

• chdman info reports the file without errors; chdman verify passes (raw + overall SHA-1).
• chdman extractraw of encoder output is byte-identical to the source (raw) and to chdman createcd output on the same CUE/BIN (CD).
• For repeated/alternating corpora the encoder's CHD files are byte-for-byte identical to chdman createraw -c zlib — deduplication and map encoding match MAME exactly.
• -c none output is byte-for-byte identical to chdman createraw -c none (including zero-hunk skipping), and chdman verify (exit 0) + extractraw round-trip it.
• Copy outputs pass chdman verify and extract byte-identically (standalone, child-source, and delta-child variants).
• Delta children made from chdman-made parents pass chdman verify -ip and byte-identical extractraw -ip.
• 100 MB+ integration tests (LargeFileValidationTests) encode 100 MB raw and ~100 MB CD images, then check chdman verify, extractraw SHA-1 vs. the source, and a deep CHDSharpLib CheckFile:

dotnet test CHDSharpEncoderTest/ --filter "FullyQualifiedName~LargeFileValidationTests"

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Performance

Encoding runs a producer→worker→consumer pipeline (HunkProcessor.CompressAll, the same shape as the library's parallel CheckFile): a single producer reads the raw hunks and maintains the running raw SHA-1, N workers (default Chd.TaskCount, 1–64, override via ChdEncodeOptions.TaskCount or CLI -t) hash and compress each hunk with private, persistent codec instances, and a single consumer writes blocks and map entries strictly in hunk order. Every codec is deterministic and dedup/offset assignment stays sequential, so the worker count can never change the output bytes (ParallelEncodeTests asserts byte-identical output across task counts).

Measured on a 24-core machine (512 MB mixed corpus, zlib): 5.1× faster with 8 workers vs. 1 (5.0 s → 0.98 s, identical 179 MB output).

For tuning and measurement today:

• ChdEncodeOptions.TaskCount (or CLI -t N) controls the worker count per encode; the default follows Chd.TaskCount, the same knob that tunes parallel verification.
• Per-hunk compression-ratio logging (ChdEncodeOptions.HunkCompleted, CLI -v).
• Memory is bounded: raw hunks and compressed results circulate through fixed-size pools sized by the worker count, so multi-GB sources encode without proportional RAM growth.

CLI

CHDSharpCli --create in.bin out.chd [-c zlib,zstd,lzma,none] [-hs 65536] [-us 4096] [-t 8] [-ip parent.chd] [-v]
CHDSharpCli --createcd in.cue out.chd [-c zlib,zstd,lzma,none] [-hs N] [-us N] [-t 8] [-ip parent.chd] [-v]
CHDSharpCli --copy in.chd out.chd [-c zlib,zstd,lzma,none] [-t 8] [-ip parent.chd] [-op parent.chd] [-v]

All commands deep-verify the result with CHDSharpLib before exiting.

Roadmap

• NRG (Nero) input parsing.
• Metadata editing (addmeta/delmeta).
• CUE style conversion / Redump matching.