transcribe-cpp-sys

Raw native FFI bindings for transcribe.cpp, a C/C++ speech-to-text library built on ggml.

Status: in development (0.0.1). This crate exposes the unsafe, generated FFI surface. Most users want the safe wrapper, transcribe-cpp.

What it does

build.rs compiles the vendored C++ tree from source via CMake (the crate tarball carries the whole tree) and reconstructs the link line from the installed transcribe-link.json manifest — no hardcoded per-platform link lists. The committed bindgen output means libclang is not needed to build this crate.

Build prerequisites

A C++ toolchain, CMake, and zlib. zlib is system-provided on Linux (zlib1g-dev) and macOS; on Windows install it with vcpkg install zlib:x64-windows-static-md (static lib against the dynamic CRT, matching Rust's default /MD on x86_64-pc-windows-msvc) and point CMAKE_PREFIX_PATH at the vcpkg install tree. The static link is the default; the shared feature links a shared library instead.

Features

metal (default on Apple), vulkan, cuda, openmp — each forwards to the matching TRANSCRIBE_* CMake option.
shared — link a shared libtranscribe (.so/.dylib/.dll) loaded at runtime instead of statically baking it in. The default is a self-contained static link.
dynamic-backends — additionally ship each compute backend (the per-ISA CPU tiers, Vulkan, CUDA, …) as a loadable module next to the library, selected at runtime by transcribe_init_backends_default() when the modules sit next to libtranscribe, or transcribe_init_backends(dir) for a custom provider directory. Implies shared.

Build-flag escape hatch

The features above cover the common, tested configurations. Anything else CMake accepts can be forwarded via the TRANSCRIBE_CMAKE_ARGS (or CMAKE_ARGS) env var — e.g. TRANSCRIBE_CMAKE_ARGS="-DGGML_VULKAN=ON" cargo build. These are split on whitespace with simple double-quote handling, applied after the feature-derived defines (so a user -D wins), and unsupported/untested by design: they exist so a Cargo feature is never a hard ceiling on what you can configure. The link line is still reconstructed from the generated manifest, so whatever you turn on links correctly.

ABI drift

The generated FFI is committed and CI-checked against include/transcribe.abihash (cargo xtask bindgen --check): a public-header ABI change turns the check red until the bindings are regenerated. Per-field layout checks are waived because bindgen takes layout from a real compiler at generation time.