Marcel Timm, RhinoDevel, 2025
mt_stt is a C++ library for Linux and Windows that offers a pure C interface to the great speech-to-text inference engine Whisper.cpp by Georgi Gerganov that itself runs OpenAI Whisper models.
With mt_stt you can:
- Transcribe from raw audio in memory to a string.
- Use a model to be loaded from file or already held in memory.
- Translate to English.
- Add an optional initial prompt (to bias/help the transcription process).
- Progress callback and cancel option.
- Optionally transcribe a specific part of the audio data, only.
- Output probabilities of the transcribed words (how sure the model is about the word representing the correct result).
After cloning the mt_stt repository, enter its folder and proceed as follows.
Get the Whisper.cpp submodule content:
git submodule update --init --recursive
No details for Linux here, yet, but you can take a look at the Windows instructions below and at the Makefile.
All the following examples are building static libraries, there may be use cases where dynamically linked libraries are sufficient, too.
Build Whisper.cpp
Compile the necessary whisper.lib and ggml.lib libraries via Visual Studio
and mt_stt/whisper.cpp/CMakeLists.txt as static libraries.
To do that, modify the file mt_stt/whisper.cpp/CMakePresets.json which is
created by Visual Studio:
If the binary of git is not in your path, modify "configurePresets" entry
with "name" "windows-base" by adding the following entry to
"cacheVariables":
"GIT_EXE": "C:\\Program Files\\Git\\bin\\git.exe"
Add entry
{
"name": "mt-x64-release-static",
"displayName": "MT x64 Release Static (native)",
"description": "MT: Target Windows (64-bit), static, with the Visual Studio development environment. (RelWithDebInfo)",
"inherits": "x64-release",
"cacheVariables": {
"BUILD_SHARED_LIBS": "OFF"
}
}
to mt_stt/whisper.cpp/CMakePresets.json's configurePresets array.
Download OpenBLAS (e.g.
OpenBLAS-0.3.29-x64.zip) and unpack the content to C:\openblas.
Additionally add entry
{
"name": "mt-x64-release-static-blas",
"displayName": "MT x64 Release Static BLAS",
"descriptio
9E12
n": "MT: Target Windows (64-bit), static, BLAS, with the Visual Studio development environment. (RelWithDebInfo)",
"inherits": "mt-x64-release-static",
"cacheVariables": {
"GGML_BLAS": "ON",
"BLAS_LIBRARIES": "C:/openblas/lib/libopenblas.lib",
"BLAS_INCLUDE_DIRS": "C:/openblas/include"
}
}
Put the libopenblas.dll (from C:\openblas\bin\libopenblas.dll) into the
folder of the executable file that will be linked with THIS project's resulting
DLL.
Working with (e.g.): CUDA 12.4.131 and Whisper.cpp v1.7.5
Additionally add entry
{
"name": "mt-x64-release-static-cuda",
"displayName": "MT x64 Release Static CUDA (native)",
"description": "MT: Target Windows (64-bit), static, CUDA, with the Visual Studio development environment. (RelWithDebInfo)",
"inherits": "mt-x64-release-static",
"cacheVariables": {
"GGML_CUDA": "ON"
}
}
to mt_stt/whisper.cpp/CMakePresets.json's configurePresets array.
In mt_stt, link with these libraries (e.g. from C:\cuda\lib\):
x64\cublas.libx64\cuda.libx64\cudart.lib
Put the following files (e.g. from C:\cuda\bin) into the folder of the
executable file that will be linked with this project's resulting DLL:
cublas64_12.dllcublasLt64_12.dllcudart64_12.dll
On a non-development PC, make sure that the most recent Nvidia drivers are installed (they include CUDA support).
Additionally add entry
{
"name": "mt-x64-release-static-sse",
"displayName": "MT x64 Release Static SSE",
"description": "MT: Target Windows (64-bit), static, SSE, with the Visual Studio development environment. (RelWithDebInfo)",
"inherits": "mt-x64-release-static",
"cacheVariables": {
"GGML_NATIVE": "OFF",
"GGML_AVX": "OFF",
"GGML_AVX2": "OFF"
}
}
to mt_stt/whisper.cpp/CMakePresets.json's configurePresets array.
and change the line
#if defined(_MSC_VER) && (defined(__AVX__) || defined(__AVX2__) || defined(__AVX512F__))
to
#if defined(_MSC_VER)// && (defined(__AVX__) || defined(__AVX2__) || defined(__AVX512F__))
in the file
mt_stt/whisper.cpp/ggml/src/ggml-cpu/ggml-cpu-impl.h
before the line
#ifndef __SSE3__
to enable SSE3 and SSSE3.
Download OpenBLAS (e.g.
OpenBLAS-0.3.29-x64.zip) and unpack the content to C:\openblas.
Additionally add entry (also don't forget ggml-cpu-impl.h - see above)
{
"name": "mt-x64-release-static-sse-blas",
"displayName": "MT x64 Release Static SSE and BLAS",
"description": "MT: Target Windows (64-bit), static, SSE, BLAS, with the Visual Studio development environment. (RelWithDebInfo)",
"inherits": "mt-x64-release-static-sse",
"cacheVariables": {
"GGML_BLAS": "ON",
"BLAS_LIBRARIES": "C:/openblas/lib/libopenblas.lib",
"BLAS_INCLUDE_DIRS": "C:/openblas/include"
}
}
Put the libopenblas.dll (from C:\openblas\bin\libopenblas.dll) into the folder
of the executable file that will be linked with this project's resulting DLL.
- Open solution
mt_stt.slnwith Visual Studio (tested with 2022). - Compile in release or debug mode.
- The sample code below is using mt_tts, which is kind of the counterpart to this project.
- Follow Test mt_tts first.
- Get the DLL and LIB files resulting from building this project, e.g. for
release mode
x64\Release\mt_stt.dllandx64\Release\mt_stt.lib, copy them to the folder from Test mt_tts. - Also copy the file
mt_stt\mt_stt.hto that folder. - Copy a Whisper(.cpp) model file that supports translation to English to the same new folder.
- Open
x64 Native Tools Command Prompt for VS 2022commandline. - Go to the example folder and put the following code into the already existing file
main.c:
#include <stdio.h>
#include <stdlib.h>
#include "mt_tts.h"
#include "mt_stt.h"
/** Example use of mt_stt transcribing & translating German language audio to
* text in English.
*
* The audio is generated first with mt_tts.
*/
int main(void)
{
int16_t* tts_result = NULL;
int sample_count = -1;
float* stt_input = NULL;
char* stt_result = NULL;
// *************************************************************************
// *** TTS: Create raw audio data from a text given in German: ***
// *************************************************************************
// Initialize TTS system with a model/voice for output in German:
mt_tts_reinit("de_DE-thorsten-high.onnx", "de_DE-thorsten-high.onnx.json");
// Get the actual raw audio data:
tts_result = mt_tts_to_raw(
"Hallo! Dies ist ein Text in deutscher Sprache. Erst wird er in ein Tonsignal umgewandelt, welches dann wiederum in Text transkribiert wird, jedoch nun auf Englisch.",
&sample_count);
// Convert the audio data into normalized floating-point representation:
stt_input = malloc(sample_count * sizeof *stt_input);
for(int i = 0; i < sample_count; ++i)
{
stt_input[i] = (float)tts_result[i] / 16384.0f;
}
// Free memory and de-initialize TTS system:
mt_tts_free_raw(tts_result);
tts_result = NULL;
mt_tts_deinit();
// *************************************************************************
// *** STT: Transcribe the audio while also translating it to English: ***
// *************************************************************************
stt_result = mt_stt_transcribe_with_file(
false,
4,
NULL,
true,
NULL,
"ggml-small-q5_1.bin",
stt_input,
sample_count,
NULL,
NULL,
NULL,
NULL,
NULL,
NULL,
0);
// Output the translated transcription of the spoken text:
printf("%s\n", stt_result);
// Free memory and exit:
free(stt_result);
stt_result = NULL;
return 0;
}
- Compile via
cl main.c mt_tts.lib mt_stt.lib. - Run
main.exe, which should show the transcription/translation result.
- Install Microsoft Visual C++ Redistributable Version for Visual Studio 2015, 2017, 2019, and 2022 (e.g. version 14.42.34433.0).