Convert OPL-family VGM/VGZ logs to DRO (DOSBox Raw OPL).
vgz2dro takes a VGM register log (or its gzip-compressed .vgz form) and rewrites
the OPL chip writes as a DRO v0.1 file (DBRAWOPL),
one .dro per input. DRO stores
both OPL register banks, so OPL3 songs convert losslessly, unlike IMF, which is
OPL2-only.
I needed to convert OPL music from opl.wafflenet.com
into DRO for the soundtracks of some retro-game rewrites, and didn't want to drag a
heavy toolchain or a pile of C/C++/Rust dependencies into such a small job. Zig hits
the sweet spot here: a single, dependency-free, cross-platform binary. The gzip
inflate uses std.compress.flate from the Zig standard library, and no libc is
linked. The resulting executable depends only on core OS libraries (no zlib, no
C runtime).
Any OPL-family chip is converted:
| Chip | VGM source |
|---|---|
| OPL2 (YM3812) | bank 0 |
| Dual OPL2 (YM3812 ×2) | chip 0 + chip 1 |
| OPL (YM3526) | bank 0 |
| Y8950 | bank 0 |
| OPL3 (YMF262) | banks 0 + 1 |
Dual OPL2 VGMs (Sound Blaster Pro and similar) are detected via the dual-chip flag in the VGM header and written with DRO hardware type Dual OPL2. Dual OPL3 (two YMF262 chips) is not fully representable in DRO v0.1; second-chip writes are captured but may not replay correctly on all players.
If the VGM header lists no OPL-family chip clock (YM2612, SN76489, OPL4 PCM, and so
on), the file is reported and skipped rather than turned into an empty or misleading
.dro. Truncated files, unknown opcodes, and invalid header offsets are rejected
with an error instead of a partial output.
Requires Zig 0.17.0-dev (see .minimum_zig_version in build.zig.zon).
zig build # -> zig-out/bin/vgz2dro[.exe]
zig build test # run unit testsvgz2dro <song.vgz|.vgm> [more files ...]Each input writes a sibling FILE.dro. Multiple files convert in one invocation.
# via the build system
zig build run -- song.vgz
# or the built binary directly
zig-out/bin/vgz2dro song1.vgz song2.vgmPer file, vgz2dro prints the detected chip, OPL register-write count, song length, and output size:
vgz2dro: song.vgz -> song.dro [OPL3, 14820 writes, 92.3 s, 31104 bytes]
vgz2dro: 1 converted, 0 skipped/failed
Input is limited to 64 MiB of decompressed VGM data.
The files this tool produces are DRO v0.1, the original DOSBox layout rather than the later v2.0 packing. The same layout was called v1.0 before DOSBox 0.73 swapped the version field names, so some tools (opal's player among them) say "DRO version 1". Either name means the same bytes. One straightforward way to hear them is the example player shipped with opal, an OPL2/OPL3 emulator:
player song.droBuild instructions live in that repository. The player also accepts HSC and IMF/WLF,
but for the output of vgz2dro the DRO path is the one that matters.
MIT. See LICENSE. Copyright (c) 2026 Bitdancer (github.com/RealBitdancer).