Files
llama.cpp/tools/mtmd/mtmd-audio.cpp
Daniel Bevenius 7e1e28cae3 mtmd : add Nemotron 3 Nano Omni support (parakeet) (#22520)
* mtmd : add Nemotron 3 Nano Omni support (parakeet)

This commit adds support for the subsampling and encoder part of
Nemotron Nemo 3 omni model.

The Parakeet subsampling/encoder were taken from parakeet.cpp which
is currently a pull request against whisper.cpp. I've tried to copy the
code a close as possible to hopefully enable easy patching between the
these two project later.

Refs: https://github.com/ggml-org/whisper.cpp/pull/3735

* mtmd : generate rel pos tensor in graph instead of in conversion [no ci]

This commit removes the generation of the relative positional tensor in
the model conversion script and instead computes it in the encoder
graph. This is only done for the window of positions required for the
current audio sample.

* mtmd : add clip_get_model to clip API [no ci]

This commit adds a function to get access to the clip_model. It also
removes the two functions clip_get_mel_filter_tensor, and
clip_get_window_tensor(const struct clip_ctx * ctx) which can now use
clip_get_model to access the model tensors that it needs.

* mtmd : read mel_filters and window into hparams

* mtmd : use set_input_f32 lambda [no ci]

* mtmd : add better asserts for mel_filters and hann window [no ci]

* mtmd : add missing size_t cast

* mtmd : change type of pad to size_t

* mtmd : zero initialize samples_padded

* mtmd : remove unsued ctx member from parakeet preprocessor

* mtmd : make log_mel_spectrogram_parakeet_worker_thread private static

* mtmd : sync/update parakeeet impl with latest whisper.cpp

This commit updates the parakeet code in mtmd to reflect the latest
updates to parakeet.cpp in whisper.cpp.

A follow up commit will address the currently hardcoded dw_pad and see
if we can add n_conv_kernel as a model metadata field.

* mtmd : add audio_conv_kernel_size to model conversion

This commit updates the model conversion to read the conv_kernel_size
field from the sound_config section of the models config.json file.
It then uses this field instead of the hardcoded values in parakeet.cpp.

* mtmd : cleanup [no ci]

* conversion : call super().filter_tensors [no ci]

* do not discard result of super filter_tensors

* mtmd : use build_mm instead of ggml_mul_mat

* mtmd : use build_ffn

* mtmd : move and reuse get_vector lambda

* mtmd : use build_inp_raw for parakeet

* mtmd : throw exception in get_scalar instead of assert

* mtmd : fix std::min call

* mtmt : use .c_str in throw clause in get_vector

* mtmd : check for F32 type and non-empty tensor in get_vector

The get_vector lambda is used by get_scalar but also standalone to read
in the mel_filters and the window data. Therefor we are not checking
for 1D tensors but allowing multiple dimensions. We do have a check in
get_scalar to verify the size of the vector.

* mtmd : replace hardcoded 1101 for n_tokens_real

* mtmd : assert subsampling_factor is 8

This commit adds an assert of the parakeet subsampling factor to check
that it is 8.

The motivation for this is that this model currently has three
convolutions with a stride of 2. If the underlying model updates the
subsampling factor these convolution operations will need to be updated
and this will produce and error if this occurs.

* mtmd : remove unused ggml_tensors attn_pos_w and mm_norm_w

* mtmd : remove single thread path

This commit removes the single thread path which was a left over from
the original parakeet.cpp where n_threads is configurable.

* fix some security issues

---------

Co-authored-by: Sigbjørn Skjæret <1629204+CISC@users.noreply.github.com>
Co-authored-by: Xuan Son Nguyen <son@huggingface.co>
2026-07-28 17:20:25 +02:00

1368 lines
50 KiB
C++

#include "mtmd-audio.h"
#define _USE_MATH_DEFINES // for M_PI
#include <cmath>
#include <cstdint>
#include <cstring>
#include <thread>
#include <vector>
#include <fstream>
#include <algorithm>
#include <functional>
// some of the code here is copied from whisper.cpp
constexpr bool DEBUG = false;
void mtmd_audio_cache::fill_sin_cos_table(uint32_t n) {
sin_vals.resize(n);
cos_vals.resize(n);
for (uint32_t i = 0; i < n; i++) {
double theta = (2 * M_PI * i) / n;
sin_vals[i] = sinf(theta);
cos_vals[i] = cosf(theta);
}
}
void mtmd_audio_cache::fill_hann_window(uint32_t length, bool periodic) {
hann_window.resize(length);
int offset = periodic ? 0 : -1;
for (uint32_t i = 0; i < length; i++) {
hann_window[i] = 0.5 * (1.0 - cosf((2.0 * M_PI * i) / (length + offset)));
}
}
void mtmd_audio_cache::fill_mel_filterbank_matrix(int64_t n_mel,
int64_t n_fft,
int sample_rate,
float fmin,
float fmax,
bool slaney_area_norm,
float scale,
bool use_htk) {
GGML_ASSERT(n_mel > 0 && n_fft > 1);
if (fmax <= 0.0f) {
fmax = 0.5f * sample_rate;
}
std::function<double(double)> hz_to_mel;
std::function<double(double)> mel_to_hz;
if (use_htk) {
hz_to_mel = [](const double f_hz) -> double {
return 2595.0 * log10(1.0 + f_hz / 700.0);
};
mel_to_hz = [](const double m) -> double {
return 700.0 * (pow(10.0, m / 2595.0) - 1.0);
};
} else {
// Slaney scale (matches librosa default)
const double min_log_hz = 1000.0;
const double lin_slope = 3 / 200.;
const double min_log_mel = min_log_hz * lin_slope;
const double log_step = log(6.4) / 27.0;
hz_to_mel = [min_log_hz, lin_slope, log_step, min_log_mel](const double f_hz) -> double {
return (f_hz < min_log_hz) ? f_hz * lin_slope : min_log_mel + log(f_hz / min_log_hz) / log_step;
};
mel_to_hz = [min_log_hz, lin_slope, log_step, min_log_mel](const double m) -> double {
return (m < min_log_mel) ? m / lin_slope : min_log_hz * exp((m - min_log_mel) * log_step);
};
}
// infer N_fft from n_fft_bins
const double bin_hz_step = double(sample_rate) / double(n_fft);
// mel grid: n_mel + 2 edges
const double m_lo = hz_to_mel(fmin);
const double m_hi = hz_to_mel(fmax);
std::vector<double> mel_pts(n_mel + 2);
for (int i = 0; i < n_mel + 2; ++i) {
mel_pts[i] = m_lo + (m_hi - m_lo) * (double(i) / (n_mel + 1));
}
// convert to Hz
std::vector<double> hz_pts(n_mel + 2);
for (int i = 0; i < n_mel + 2; ++i) {
hz_pts[i] = mel_to_hz(mel_pts[i]);
}
const int64_t n_fft_bins = n_fft / 2 + 1;
// Validate allocation size
if ((size_t)n_mel * (size_t)n_fft_bins > SIZE_MAX) {
GGML_ASSERT(false && "mel filterbank allocation too large");
}
// filterbank
std::vector<float> out((size_t)n_mel * (size_t)n_fft_bins, 0);
for (int64_t m = 0; m < n_mel; ++m) {
const double f_left = hz_pts[m];
const double f_center = hz_pts[m + 1];
const double f_right = hz_pts[m + 2];
const double denom_l = std::max(1e-30, f_center - f_left);
const double denom_r = std::max(1e-30, f_right - f_center);
const double enorm = slaney_area_norm ? (2.0 / std::max(1e-30, f_right - f_left)) : 1.0;
for (int k = 0; k < n_fft_bins; ++k) {
const double f = k * bin_hz_step;
double w = 0.0;
if (f >= f_left && f <= f_center) {
w = (f - f_left) / denom_l;
} else if (f > f_center && f <= f_right) {
w = (f_right - f) / denom_r;
}
out[size_t(m) * size_t(n_fft_bins) + size_t(k)] = float(w * enorm * scale);
}
}
filters.n_mel = n_mel;
filters.n_fft = n_fft;
filters.data = std::move(out);
if (DEBUG) { // debug
for (size_t i = 0; i < filters.data.size(); ++i) {
if (filters.data[i] != 0.0f) {
printf("filters[%zu] = %f\n", i, filters.data[i] * 1000.0f);
}
}
}
}
// Unified DFT implementation for both forward and inverse transforms
// Template parameters:
// Inverse: false = DFT with exp(-2πi·k·n/N), no scaling
// true = IDFT with exp(+2πi·k·n/N), scales by 1/N
// RealInput: true = input is real-valued (stride 1), avoids imaginary computations
// false = input is complex-valued (interleaved real/imag, stride 2)
template <bool Inverse, bool RealInput>
static void dft_impl(const mtmd_audio_cache & cache, const float * in, int N, float * out) {
const int n_sin_cos_vals = cache.sin_vals.size();
const int sin_cos_step = n_sin_cos_vals / N;
constexpr float sign = Inverse ? 1.0f : -1.0f;
const float scale = Inverse ? (1.0f / N) : 1.0f;
for (int k = 0; k < N; k++) {
float re = 0;
float im = 0;
for (int n = 0; n < N; n++) {
int idx = (k * n * sin_cos_step) % n_sin_cos_vals;
float cos_val = cache.cos_vals[idx];
float sin_val = cache.sin_vals[idx];
if constexpr (RealInput) {
// Real input: in_im = 0, simplifies to:
// re += in_re * cos_val
// im += sign * in_re * sin_val
float in_re = in[n];
re += in_re * cos_val;
im += sign * in_re * sin_val;
} else {
float in_re = in[n * 2 + 0];
float in_im = in[n * 2 + 1];
// (a + bi) * (cos + sign*i*sin) = (a*cos - sign*b*sin) + (sign*a*sin + b*cos)i
re += in_re * cos_val - sign * in_im * sin_val;
im += sign * in_re * sin_val + in_im * cos_val;
}
}
out[k * 2 + 0] = re * scale;
out[k * 2 + 1] = im * scale;
}
}
// Cooley-Tukey FFT/IFFT unified implementation
// Template parameters:
// Inverse: false = FFT with exp(-2πi·k/N), no scaling
// true = IFFT with exp(+2πi·k/N), scales by 0.5 at each level
// RealInput: true = input is real-valued (stride 1)
// false = input is complex-valued (interleaved real/imag, stride 2)
template <bool Inverse, bool RealInput>
static void fft_impl(const mtmd_audio_cache & cache, float * in, int N, float * out) {
GGML_ASSERT(N > 0);
const int n_sin_cos_vals = cache.sin_vals.size();
if (N == 1) {
out[0] = in[0];
if constexpr (RealInput) {
out[1] = 0.0f;
} else {
out[1] = in[1];
}
return;
}
const int half_N = N / 2;
if (N - half_N * 2 == 1) {
// Odd N: fall back to DFT
dft_impl<Inverse, RealInput>(cache, in, N, out);
return;
}
// Split into even and odd
if constexpr (RealInput) {
// Real input: stride is 1, copy only real values
float * even = in + N;
for (int i = 0; i < half_N; ++i) {
even[i] = in[2 * i];
}
float * even_fft = out + 2 * N;
fft_impl<Inverse, true>(cache, even, half_N, even_fft);
float * odd = even;
for (int i = 0; i < half_N; ++i) {
odd[i] = in[2 * i + 1];
}
float * odd_fft = even_fft + N;
fft_impl<Inverse, true>(cache, odd, half_N, odd_fft);
} else {
// Complex input: stride is 2, copy complex pairs
float * even = in + N * 2;
for (int i = 0; i < half_N; ++i) {
even[i * 2 + 0] = in[2 * i * 2 + 0];
even[i * 2 + 1] = in[2 * i * 2 + 1];
}
float * even_fft = out + 2 * N;
fft_impl<Inverse, false>(cache, even, half_N, even_fft);
float * odd = even;
for (int i = 0; i < half_N; ++i) {
odd[i * 2 + 0] = in[(2 * i + 1) * 2 + 0];
odd[i * 2 + 1] = in[(2 * i + 1) * 2 + 1];
}
float * odd_fft = even_fft + N;
fft_impl<Inverse, false>(cache, odd, half_N, odd_fft);
}
float * even_fft = out + 2 * N;
float * odd_fft = even_fft + N;
const int sin_cos_step = n_sin_cos_vals / N;
constexpr float sign = Inverse ? 1.0f : -1.0f;
constexpr float scale = Inverse ? 0.5f : 1.0f;
for (int k = 0; k < half_N; k++) {
int idx = k * sin_cos_step; // t = 2*M_PI*k/N
float re = cache.cos_vals[idx];
float im = sign * cache.sin_vals[idx];
float re_odd = odd_fft[2 * k + 0];
float im_odd = odd_fft[2 * k + 1];
out[2 * k + 0] = scale * (even_fft[2 * k + 0] + re * re_odd - im * im_odd);
out[2 * k + 1] = scale * (even_fft[2 * k + 1] + re * im_odd + im * re_odd);
out[2 * (k + half_N) + 0] = scale * (even_fft[2 * k + 0] - re * re_odd + im * im_odd);
out[2 * (k + half_N) + 1] = scale * (even_fft[2 * k + 1] - re * im_odd - im * re_odd);
}
}
// Forward FFT for real input (used by mel spectrogram)
static void fft(const mtmd_audio_cache & cache, float * in, int N, float * out) {
fft_impl<false, true>(cache, in, N, out);
}
// Inverse FFT for complex input
static void ifft(const mtmd_audio_cache & cache, float * in, int N, float * out) {
fft_impl<true, false>(cache, in, N, out);
}
struct filter_params {
int64_t n_mel;
int64_t n_fft_bins;
int32_t hann_window_size;
int32_t hop_length;
int32_t sample_rate;
bool no_padding = false;
bool center_padding = false;
float preemph = 0.f;
bool use_natural_log = false;
bool norm_per_feature = false;
bool use_magnitude = false; // |X| instead of |X|^2
float mel_floor = 5.960464477539063e-08f;
};
static void log_mel_spectrogram_worker_thread(int ith,
const float * hann,
const std::vector<float> & samples,
int n_samples,
int frame_size,
int frame_step,
int n_threads,
const filter_params & params,
const mtmd_audio_cache & cache,
mtmd_audio_mel & out) {
std::vector<float> fft_in(frame_size * 2, 0.0);
std::vector<float> fft_out(frame_size * 2 * 2 * 2);
int64_t n_fft_bins = params.n_fft_bins;
int64_t i = ith;
const auto & filters = cache.filters;
// make sure n_fft == 1 + (WHISPER_N_FFT / 2), bin_0 to bin_nyquist
GGML_ASSERT(n_fft_bins == 1 + (frame_size / 2));
GGML_ASSERT(cache.sin_vals.size() == cache.cos_vals.size());
// calculate FFT only when fft_in are not all zero
for (; i < std::min((int64_t)(n_samples / frame_step + 1), out.n_len); i += n_threads) {
const int64_t offset = i * frame_step;
// apply Hann window (~10% faster)
const int valid_len = std::min(frame_size, std::max(0, n_samples - (int)offset));
for (int j = 0; j < valid_len; j++) {
fft_in[j] = hann[j] * samples[offset + j];
}
// fill the rest with zeros
if (valid_len < frame_size) {
std::fill(fft_in.begin() + valid_len, fft_in.end(), 0.0);
}
// FFT
fft(cache, fft_in.data(), frame_size, fft_out.data());
// Calculate modulus^2 (power) or modulus (magnitude)
for (int j = 0; j < n_fft_bins; j++) {
float power = (fft_out[2 * j + 0] * fft_out[2 * j + 0] + fft_out[2 * j + 1] * fft_out[2 * j + 1]);
fft_out[j] = params.use_magnitude ? sqrtf(power) : power;
}
// mel spectrogram
for (int64_t j = 0; j < out.n_mel; j++) {
double sum = 0.0;
// unroll loop (suggested by GH user @lunixbochs)
int k = 0;
for (k = 0; k < n_fft_bins - 3; k += 4) {
size_t idx = size_t(j) * size_t(n_fft_bins) + size_t(k);
sum +=
fft_out[k + 0] * filters.data[idx + 0] +
fft_out[k + 1] * filters.data[idx + 1] +
fft_out[k + 2] * filters.data[idx + 2] +
fft_out[k + 3] * filters.data[idx + 3];
}
// handle n_fft remainder
for (; k < n_fft_bins; k++) {
sum += fft_out[k] * filters.data[(size_t)j * n_fft_bins + k];
}
sum = std::max(sum, (double)params.mel_floor);
sum = params.use_natural_log
? log(sum)
: log10(sum);
out.data[(size_t)j * out.n_len + i] = sum;
}
}
// Otherwise fft_out are all zero
double sum = params.use_natural_log ? log(1e-10) : log10(1e-10);
for (; i < out.n_len; i += n_threads) {
for (int64_t j = 0; j < out.n_mel; j++) {
out.data[(size_t)j * out.n_len + i] = sum;
}
}
}
// ref: https://github.com/openai/whisper/blob/main/whisper/audio.py#L110-L157
static bool log_mel_spectrogram(
const float * samples,
const int n_samples_in,
const int n_threads,
const filter_params & params,
const mtmd_audio_cache & cache,
mtmd_audio_mel & out) {
//const int64_t t_start_us = ggml_time_us();
out.n_len_org = n_samples_in;
int n_samples = n_samples_in;
// Hann window
const float * hann = cache.hann_window.data();
const int frame_size = (params.n_fft_bins - 1) * 2;
const int frame_step = params.hop_length;
// Padding
std::vector<float> samples_padded;
if (params.no_padding) {
// no padding, use samples as-is
samples_padded = std::vector<float>(samples, samples + n_samples);
samples = samples_padded.data();
n_samples = samples_padded.size();
} else if (params.center_padding) {
const auto pad_amount = frame_size / 2;
samples_padded = std::vector<float>(n_samples + 2 * pad_amount, 0);
std::copy(samples, samples + n_samples, samples_padded.data() + pad_amount);
samples = samples_padded.data();
n_samples = samples_padded.size();
} else {
// existing padding logic
int64_t stage_1_pad = params.sample_rate * 30;
int64_t stage_2_pad = frame_size / 2;
samples_padded.resize(n_samples + stage_1_pad + stage_2_pad * 2);
std::copy(samples, samples + n_samples, samples_padded.begin() + stage_2_pad);
// pad 30 seconds of zeros at the end of audio (480,000 samples) + reflective pad 200 samples at the end of audio
std::fill(samples_padded.begin() + n_samples + stage_2_pad, samples_padded.begin() + n_samples + stage_1_pad + 2 * stage_2_pad, 0);
// reflective pad 200 samples at the beginning of audio
if (n_samples < stage_2_pad + 1) {
// TODO: Handle short audio differently or return error
return false;
}
std::reverse_copy(samples + 1, samples + 1 + stage_2_pad, samples_padded.begin());
// expose the padded buffer to downstream FFT and to out.n_len computation
// mirrors the no_padding and center_padding branches above
samples = samples_padded.data();
n_samples = samples_padded.size();
}
// preemphasis
if (params.preemph) {
const int pad_amount = frame_size / 2;
const float preemph = 0.97f;
float prev = samples_padded[pad_amount];
for (int i = pad_amount + 1; i + pad_amount < n_samples; ++i) {
float cur = samples_padded[i];
samples_padded[i] = cur - preemph * prev;
prev = cur;
}
}
// pad hann window if it's smaller than frame_size
// TODO: probably unnecessary here? (or better doing it in g_cache?)
std::vector<float> hann_window_padded;
if (params.hann_window_size < frame_size) {
hann_window_padded.resize(frame_size);
const int padding = (frame_size - params.hann_window_size) / 2;
std::copy(hann, hann + params.hann_window_size, &hann_window_padded[padding]);
hann = hann_window_padded.data();
}
GGML_ASSERT(params.n_fft_bins > 0);
GGML_ASSERT(params.hop_length > 0);
out.n_mel = params.n_mel;
out.n_len = (n_samples - frame_size) / frame_step + 1;
// Validate dimensions before allocation to prevent integer overflow
if (out.n_mel <= 0 || out.n_len <= 0) {
LOG_ERR("%s: invalid mel dimensions n_mel=%lld n_len=%lld\n", __func__, (long long)out.n_mel, (long long)out.n_len);
return false;
}
const size_t total_size = (size_t)out.n_mel * (size_t)out.n_len;
if (total_size > SIZE_MAX / sizeof(float)) {
LOG_ERR("%s: size overflow: n_mel=%lld n_len=%lld\n", __func__, (long long)out.n_mel, (long long)out.n_len);
return false;
}
if (n_samples < frame_size) {
LOG_ERR("%s: not enough samples after padding\n", __func__);
return false;
}
out.data.resize(total_size);
{
std::vector<std::thread> workers(n_threads - 1);
for (int iw = 0; iw < n_threads - 1; ++iw) {
workers[iw] =
std::thread(log_mel_spectrogram_worker_thread, iw + 1, hann, std::cref(samples_padded), n_samples,
frame_size, frame_step, n_threads, std::cref(params), std::cref(cache), std::ref(out));
}
// main thread
log_mel_spectrogram_worker_thread(0, hann, samples_padded, n_samples, frame_size, frame_step, n_threads, params,
cache, out);
for (int iw = 0; iw < n_threads - 1; ++iw) {
workers[iw].join();
}
}
const int64_t effective_n_len = n_samples_in / frame_step;
if (params.norm_per_feature) {
GGML_ASSERT(effective_n_len > 1);
for (int64_t i = 0; i < out.n_mel; i++) {
double mean = 0;
for (int64_t j = 0; j < effective_n_len; ++j) {
mean += out.data[(size_t)i * out.n_len + j];
}
mean /= effective_n_len;
double var = 0.0;
for (int64_t j = 0; j < effective_n_len; ++j) {
const double value = out.data[(size_t)i * out.n_len + j] - mean;
var += value * value;
}
var /= effective_n_len - 1; // unbiased
const double mstd = std::sqrt(var + 1e-5);
for (int64_t j = 0; j < effective_n_len; ++j) {
auto &value = out.data[(size_t)i * out.n_len + j];
value = (value - mean) / mstd;
}
// pad the rest with zeros
for (int64_t j = effective_n_len; j < out.n_len; ++j) {
out.data[(size_t)i * out.n_len + j] = 0.0;
}
}
} else if (!params.no_padding) {
// Whisper-style clamping and normalization (NOT used by Gemma4)
double mmax = -1e20;
const size_t mel_size = (size_t)out.n_mel * (size_t)out.n_len;
for (size_t i = 0; i < mel_size; i++) {
if (out.data[i] > mmax) {
mmax = out.data[i];
}
}
mmax -= 8.0;
for (size_t i = 0; i < mel_size; i++) {
if (out.data[i] < mmax) {
out.data[i] = mmax;
}
out.data[i] = (out.data[i] + 4.0)/4.0;
}
}
// Dump log_mel_spectrogram
if (DEBUG) {
std::ofstream outFile("log_mel_spectrogram.json");
outFile << "[";
for (uint64_t i = 0; i < out.data.size() - 1; i++) {
outFile << out.data[i] << ", ";
}
outFile << out.data[out.data.size() - 1] << "]";
outFile.close();
}
return true;
}
//
// mtmd_audio_preprocessor_whisper
//
void mtmd_audio_preprocessor_whisper::initialize() {
cache.fill_sin_cos_table(hparams.audio_n_fft);
cache.fill_hann_window(hparams.audio_window_len, true);
cache.fill_mel_filterbank_matrix(hparams.n_mel_bins, hparams.audio_n_fft, hparams.audio_sample_rate);
}
bool mtmd_audio_preprocessor_whisper::preprocess(const float * samples,
size_t n_samples,
std::vector<mtmd_audio_mel> & output) {
if (n_samples == 0) {
// empty audio
return false;
}
std::vector<float> smpl;
// if input is too short, pad with zeros
// this is to avoid potential issues with stage1/2 padding in log_mel_spectrogram
// TODO: maybe handle this better
size_t min_samples = (size_t) hparams.audio_sample_rate * (hparams.audio_chunk_len + 1); // +1 second margin
if (n_samples < min_samples) {
smpl.resize(min_samples, 0.0f);
std::memcpy(smpl.data(), samples, n_samples * sizeof(float));
samples = smpl.data();
n_samples = smpl.size();
}
filter_params params;
params.n_mel = hparams.n_mel_bins;
params.n_fft_bins = 1 + (hparams.audio_n_fft / 2);
params.hann_window_size = hparams.audio_window_len;
params.hop_length = hparams.audio_hop_len;
params.sample_rate = hparams.audio_sample_rate;
params.center_padding = false;
params.preemph = 0.0f; // disabled
params.use_natural_log = false;
params.norm_per_feature = false;
// make sure the cache is initialized
GGML_ASSERT(!cache.sin_vals.empty());
GGML_ASSERT(!cache.cos_vals.empty());
GGML_ASSERT(!cache.filters.data.empty());
mtmd_audio_mel out_full;
bool ok = log_mel_spectrogram(samples, n_samples,
4, // n_threads
params, cache, out_full);
if (!ok) {
return false;
}
// because the cgraph in clip.cpp only accepts 3000 frames each, we need to split the mel
// we always expect the mel to have 3000 silent frames at the end
if (DEBUG) {
printf("output: n_mel = %d, n_len = %d\n", (int) out_full.n_mel, (int) out_full.n_len);
}
const size_t frames_per_chunk = 3000;
GGML_ASSERT((size_t) out_full.n_len > frames_per_chunk);
for (size_t off = 0; off < (size_t) out_full.n_len; off += frames_per_chunk) {
int64_t n_len = std::min((int64_t)frames_per_chunk, out_full.n_len - (int64_t)off);
if (n_len < (int64_t)frames_per_chunk) {
break; // last incomplete chunk will always be a padded chunk, safe to ignore
}
mtmd_audio_mel out_chunk;
out_chunk.n_len = n_len;
out_chunk.n_mel = out_full.n_mel;
out_chunk.n_len_org = out_full.n_mel; // unused
out_chunk.data.reserve((size_t)out_chunk.n_mel * (size_t)out_chunk.n_len);
for (int64_t i = 0; i < out_full.n_mel; i++) {
auto src = out_full.data.begin() + (size_t)i * out_full.n_len + off;
out_chunk.data.insert(out_chunk.data.end(), src, src + frames_per_chunk);
}
output.push_back(std::move(out_chunk));
}
return true;
}
//
// mtmd_audio_preprocessor_qwen3a
//
// Matches the Python WhisperFeatureExtractor called with truncation=False:
// - reflection padding of n_fft/2 samples at each end (center=True)
// - Whisper-style log10 + (max-8)/4 normalization applied to full audio
// - output split into ≤30s (3000 mel frames) windows, each padded to a
// multiple of 200 frames (n_window * 2) for the cgraph batch view
//
void mtmd_audio_preprocessor_qwen3a::initialize() {
cache.fill_sin_cos_table(hparams.audio_n_fft);
cache.fill_hann_window(hparams.audio_window_len, true);
cache.fill_mel_filterbank_matrix(hparams.n_mel_bins, hparams.audio_n_fft, hparams.audio_sample_rate);
}
bool mtmd_audio_preprocessor_qwen3a::preprocess(const float * samples,
size_t n_samples,
std::vector<mtmd_audio_mel> & output) {
if (n_samples == 0) {
return false;
}
GGML_ASSERT(!cache.sin_vals.empty());
GGML_ASSERT(!cache.cos_vals.empty());
GGML_ASSERT(!cache.filters.data.empty());
// Reflection-pad n_fft/2 samples at each end, matching WhisperFeatureExtractor center=True
const int pad = hparams.audio_n_fft / 2; // = 200
std::vector<float> padded(n_samples + 2 * pad, 0.0f);
// Reflect start: padded[0..pad-1] = samples[pad..1] (reversed)
for (int i = 0; i < pad; i++) {
int src = pad - i; // samples[pad], samples[pad-1], ..., samples[1]
padded[i] = (src < (int)n_samples) ? samples[src] : 0.0f;
}
std::copy(samples, samples + n_samples, padded.begin() + pad);
// Reflect end: padded[n+pad..n+2*pad-1] = samples[n-2..n-pad-1] (reversed)
for (int i = 0; i < pad; i++) {
int src = (int)n_samples - 2 - i; // samples[n-2], samples[n-3], ...
padded[n_samples + pad + i] = (src >= 0) ? samples[src] : 0.0f;
}
filter_params params;
params.n_mel = hparams.n_mel_bins;
params.n_fft_bins = 1 + (hparams.audio_n_fft / 2);
params.hann_window_size = hparams.audio_window_len;
params.hop_length = hparams.audio_hop_len;
params.sample_rate = hparams.audio_sample_rate;
params.no_padding = true; // reflection padding already applied above
params.use_natural_log = false; // log10
mtmd_audio_mel mel_full;
bool ok = log_mel_spectrogram(padded.data(), (int)padded.size(), 4, params, cache, mel_full);
if (!ok) {
return false;
}
// Whisper-style normalization: clamp to (max - 8), scale to [-1, 1]
{
double mmax = -1e20;
for (float v : mel_full.data) {
if (v > mmax) mmax = v;
}
mmax -= 8.0;
for (float & v : mel_full.data) {
v = (std::max((double)v, mmax) + 4.0) / 4.0;
}
}
// The effective frame count: center-padded STFT gives ~n_samples/hop_length frames.
// We take min(mel_full.n_len, n_samples/hop + 1) to avoid including excess frames.
const int64_t n_eff = std::min(mel_full.n_len,
(int64_t)(n_samples / hparams.audio_hop_len) + 1);
// Split into inference windows matching n_window_infer=800 from model config.
// Each window is padded to the next multiple of chunk_size for the cgraph.
// The mtmd caller loops over output entries, so long audio is handled automatically.
const int chunk_size = 100; // conv sub-chunk size (n_window * 2, n_window=50)
const int window_size = 800; // mel frames per forward pass (n_window_infer=800)
for (int64_t off = 0; off < n_eff; off += window_size) {
const int64_t win_eff = std::min((int64_t)window_size, n_eff - off);
const int64_t n_chunks = (win_eff + chunk_size - 1) / chunk_size;
const int64_t n_padded = n_chunks * chunk_size;
mtmd_audio_mel out;
out.n_mel = mel_full.n_mel;
out.n_len = n_padded;
out.n_len_org = win_eff;
out.data.assign((size_t)out.n_mel * (size_t)out.n_len, 0.0f);
for (int64_t m = 0; m < out.n_mel; m++) {
const int64_t copy_len = std::min((int64_t)win_eff, mel_full.n_len - off);
if (copy_len > 0) {
std::copy(mel_full.data.begin() + (size_t)m * mel_full.n_len + off,
mel_full.data.begin() + (size_t)m * mel_full.n_len + off + copy_len,
out.data.begin() + (size_t)m * out.n_len);
}
}
output.push_back(std::move(out));
}
return true;
}
//
// mtmd_audio_preprocessor_mimo_audio
//
// Matches torchaudio.transforms.MelSpectrogram(power=1.0, center=True) followed by
// log(clip(spec, min=1e-7)): HTK mel scale, no Slaney area norm, magnitude (not power)
// spectrogram, natural log, reflect-padded by n_fft/2 on each side.
//
void mtmd_audio_preprocessor_mimo_audio::initialize() {
cache.fill_sin_cos_table(hparams.audio_n_fft);
cache.fill_hann_window(hparams.audio_window_len, true);
cache.fill_mel_filterbank_matrix(
hparams.n_mel_bins, hparams.audio_n_fft, hparams.audio_sample_rate,
0.0f, hparams.audio_sample_rate / 2.0f,
/*slaney_area_norm=*/ false,
/*scale=*/ 1.0f,
/*use_htk=*/ true
);
}
bool mtmd_audio_preprocessor_mimo_audio::preprocess(const float * samples,
size_t n_samples,
std::vector<mtmd_audio_mel> & output) {
if (n_samples == 0) {
return false;
}
GGML_ASSERT(!cache.sin_vals.empty());
GGML_ASSERT(!cache.cos_vals.empty());
GGML_ASSERT(!cache.filters.data.empty());
const int pad = hparams.audio_n_fft / 2;
std::vector<float> padded(n_samples + 2 * pad, 0.0f);
for (int i = 0; i < pad; i++) {
int src = pad - i;
padded[i] = (src < (int)n_samples) ? samples[src] : 0.0f;
}
std::copy(samples, samples + n_samples, padded.begin() + pad);
for (int i = 0; i < pad; i++) {
int src = (int)n_samples - 2 - i;
padded[n_samples + pad + i] = (src >= 0) ? samples[src] : 0.0f;
}
filter_params params;
params.n_mel = hparams.n_mel_bins;
params.n_fft_bins = 1 + (hparams.audio_n_fft / 2);
params.hann_window_size = hparams.audio_window_len;
params.hop_length = hparams.audio_hop_len;
params.sample_rate = hparams.audio_sample_rate;
params.no_padding = true; // reflect padding already applied above
params.use_natural_log = true;
params.use_magnitude = true;
params.mel_floor = 1e-7f;
params.norm_per_feature = false;
mtmd_audio_mel out;
bool ok = log_mel_spectrogram(padded.data(), (int)padded.size(), 4, params, cache, out);
if (!ok) {
return false;
}
output.push_back(std::move(out));
return true;
}
//
// mtmd_audio_preprocessor_conformer
//
void mtmd_audio_preprocessor_conformer::initialize() {
cache.fill_sin_cos_table(hparams.audio_n_fft);
cache.fill_hann_window(hparams.audio_window_len, true);
cache.fill_mel_filterbank_matrix(hparams.n_mel_bins, hparams.audio_n_fft, hparams.audio_sample_rate);
}
bool mtmd_audio_preprocessor_conformer::preprocess(const float * samples,
size_t n_samples,
std::vector<mtmd_audio_mel> & output) {
// empty audio
if (n_samples == 0) {
return false;
}
filter_params params;
params.n_mel = hparams.n_mel_bins;
params.n_fft_bins = 1 + (hparams.audio_n_fft / 2);
params.hann_window_size = hparams.audio_window_len;
params.hop_length = hparams.audio_hop_len;
params.sample_rate = hparams.audio_sample_rate;
params.center_padding = true;
params.preemph = 0.97f;
params.use_natural_log = true;
params.norm_per_feature = true;
// make sure the cache is initialized
GGML_ASSERT(!cache.sin_vals.empty());
GGML_ASSERT(!cache.cos_vals.empty());
GGML_ASSERT(!cache.filters.data.empty());
mtmd_audio_mel out_full;
bool ok = log_mel_spectrogram(samples, n_samples,
4, // n_threads
params, cache, out_full);
if (!ok) {
return false;
}
output.push_back(std::move(out_full));
return true;
}
//
// mtmd_audio_preprocessor_granite_speech
//
void mtmd_audio_preprocessor_granite_speech::initialize() {
cache.fill_sin_cos_table(hparams.audio_n_fft);
cache.fill_hann_window(hparams.audio_window_len, true);
cache.fill_mel_filterbank_matrix(
hparams.n_mel_bins / 2, hparams.audio_n_fft, hparams.audio_sample_rate,
0.0f, -1.0f, false, 1.0f, true);
}
bool mtmd_audio_preprocessor_granite_speech::preprocess(const float * samples,
size_t n_samples,
std::vector<mtmd_audio_mel> & output) {
if (n_samples == 0) {
return false;
}
GGML_ASSERT(!cache.sin_vals.empty());
GGML_ASSERT(!cache.cos_vals.empty());
GGML_ASSERT(!cache.filters.data.empty());
const int n_fft = hparams.audio_n_fft;
const int pad = n_fft / 2;
// reflect padding
const int n_padded = (int)n_samples + 2 * pad;
std::vector<float> padded(n_padded, 0.0f);
std::copy(samples, samples + n_samples, padded.data() + pad);
for (int i = 0; i < pad; i++) {
int src = i + 1;
if (src >= (int)n_samples) {
src = (int)n_samples - 1;
}
padded[pad - 1 - i] = samples[src];
}
for (int i = 0; i < pad; i++) {
int src = (int)n_samples - 2 - i;
if (src < 0) {
src = 0;
}
padded[pad + (int)n_samples + i] = samples[src];
}
filter_params params;
params.n_mel = hparams.n_mel_bins / 2;
params.n_fft_bins = 1 + (n_fft / 2);
params.hann_window_size = hparams.audio_window_len;
params.hop_length = hparams.audio_hop_len;
params.sample_rate = hparams.audio_sample_rate;
params.no_padding = true;
params.center_padding = false;
params.preemph = 0.0f;
params.use_natural_log = false;
params.norm_per_feature = false;
params.mel_floor = 1e-10f;
mtmd_audio_mel mel;
if (!log_mel_spectrogram(padded.data(), n_padded, 4, params, cache, mel)) {
return false;
}
double mmax = -1e20;
const size_t mel_size = (size_t)mel.n_mel * (size_t)mel.n_len;
for (size_t i = 0; i < mel_size; i++) {
if (mel.data[i] > mmax) {
mmax = mel.data[i];
}
}
mmax -= 8.0;
for (size_t i = 0; i < mel_size; i++) {
if (mel.data[i] < mmax) {
mel.data[i] = mmax;
}
mel.data[i] = (mel.data[i] + 4.0) / 4.0;
}
int64_t n_frames = mel.n_len;
if (n_frames % 2 == 1) {
n_frames--;
}
const int64_t n_mel = mel.n_mel;
const int64_t n_stacked = n_frames / 2;
mtmd_audio_mel stacked;
stacked.n_mel = 2 * n_mel;
stacked.n_len = n_stacked;
stacked.n_len_org = (int64_t)n_samples;
stacked.data.resize((size_t)2 * (size_t)n_mel * (size_t)n_stacked);
for (int64_t t = 0; t < n_stacked; t++) {
for (int64_t m = 0; m < n_mel; m++) {
stacked.data[(size_t)m * n_stacked + t] = mel.data[(size_t)m * mel.n_len + 2 * t];
stacked.data[(size_t)(m + n_mel) * n_stacked + t] = mel.data[(size_t)m * mel.n_len + 2 * t + 1];
}
}
output.push_back(std::move(stacked));
return true;
}
//
// mtmd_audio_preprocessor_gemma4a
//
void mtmd_audio_preprocessor_gemma4a::initialize() {
cache.fill_sin_cos_table(hparams.audio_n_fft);
// Standard periodic Hann window, zero-padded to FFT size
cache.hann_window.assign(hparams.audio_n_fft, 0.0f);
for (uint32_t i = 0; i < (uint32_t)hparams.audio_window_len; i++) {
cache.hann_window[i] = 0.5f - 0.5f * cosf((2.0f * (float)M_PI * i) / hparams.audio_window_len);
}
// HTK mel scale, no Slaney area normalization
cache.fill_mel_filterbank_matrix(
hparams.n_mel_bins, hparams.audio_n_fft, hparams.audio_sample_rate,
0.0f, hparams.audio_sample_rate / 2.0f,
/*slaney_area_norm=*/ false,
/*scale=*/ 1.0f,
/*use_htk=*/ true
);
}
bool mtmd_audio_preprocessor_gemma4a::preprocess(const float * samples,
size_t n_samples,
std::vector<mtmd_audio_mel> & output) {
if (n_samples == 0) {
return false;
}
GGML_ASSERT(!cache.sin_vals.empty());
GGML_ASSERT(!cache.cos_vals.empty());
GGML_ASSERT(!cache.filters.data.empty());
filter_params params;
params.n_mel = hparams.n_mel_bins;
params.n_fft_bins = 1 + (hparams.audio_n_fft / 2);
params.hann_window_size = hparams.audio_n_fft; // window is zero-padded to FFT size
params.hop_length = hparams.audio_hop_len;
params.sample_rate = hparams.audio_sample_rate;
params.no_padding = true;
params.center_padding = false;
params.preemph = 0.0f;
params.use_natural_log = true;
params.use_magnitude = true;
params.mel_floor = 0.001f;
params.norm_per_feature = false;
// Split into 30-second chunks (model context limit, ~750 tokens each)
const size_t chunk_samples = 30 * hparams.audio_sample_rate;
for (size_t off = 0; off < n_samples; off += chunk_samples) {
const float * chunk_ptr = samples + off;
size_t chunk_len = std::min(chunk_samples, n_samples - off);
// Semicausal left-padding + right-padding to match PyTorch frame count
const int pad_left = hparams.audio_window_len / 2;
const int fft_size = hparams.audio_n_fft;
const int hop = hparams.audio_hop_len;
const int n_with_left = (int)chunk_len + pad_left;
// PyTorch: unfold(size=frame_length+1, step=hop) on semicausal-padded waveform
const int64_t pt_frames = (n_with_left - (hparams.audio_window_len + 1)) / hop + 1;
const int64_t n_padded_needed = (pt_frames - 1) * hop + fft_size;
const int total_pad = std::max((int)(n_padded_needed - (int)chunk_len), pad_left);
std::vector<float> padded_samples(total_pad + chunk_len, 0.0f);
std::copy(chunk_ptr, chunk_ptr + chunk_len, padded_samples.data() + pad_left);
mtmd_audio_mel out_chunk;
bool ok = log_mel_spectrogram(padded_samples.data(), padded_samples.size(), 4, params, cache, out_chunk);
if (!ok) {
return false;
}
// Trim to PyTorch frame count
out_chunk.n_len = std::min(out_chunk.n_len, pt_frames);
output.push_back(std::move(out_chunk));
}
return true;
}
//
// mtmd_audio_preprocessor_parakeet implementation
//
void mtmd_audio_preprocessor_parakeet::worker_thread(
int ith,
const float * window_func,
int window_size,
const std::vector<float> & samples,
int n_samples,
int frame_size,
int frame_step,
int n_threads,
int n_fft_bins,
const mtmd_audio_cache & cache,
mtmd_audio_mel & mel) {
std::vector<float> fft_in(frame_size * 2, 0.0);
std::vector<float> fft_out(frame_size * 2 * 2 * 2);
int n_fb = n_fft_bins;
int i = ith;
GGML_ASSERT(n_fb == 1 + (frame_size / 2));
const double eps = 5.960464477539063e-08;
for (; i < std::min(n_samples / frame_step + 1, (int) mel.n_len); i += n_threads) {
const int offset = i * frame_step;
const int window_pad_left = (frame_size - window_size) / 2;
// Zero-pad left.
std::fill(fft_in.begin(), fft_in.begin() + window_pad_left, 0.0f);
// Apply windowed samples in the center.
const int n_to_process = std::min({window_size, n_samples - offset});
for (int j = 0; j < n_to_process; j++) {
fft_in[window_pad_left + j] = window_func[j] * samples[offset + window_pad_left + j];
}
// Zero-pad right.
std::fill(fft_in.begin() + window_pad_left + n_to_process, fft_in.begin() + frame_size, 0.0f);
// FFT.
fft(cache, fft_in.data(), frame_size, fft_out.data());
// Calculate modulus^2 of complex numbers.
for (int j = 0; j < n_fb; j++) {
fft_out[j] = (fft_out[2 * j + 0] * fft_out[2 * j + 0] + fft_out[2 * j + 1] * fft_out[2 * j + 1]);
}
// mel spectrogram.
for (int j = 0; j < mel.n_mel; j++) {
double sum = 0.0;
int k = 0;
for (k = 0; k < n_fb - 3; k += 4) {
sum +=
fft_out[k + 0] * cache.filters.data[j * n_fb + k + 0] +
fft_out[k + 1] * cache.filters.data[j * n_fb + k + 1] +
fft_out[k + 2] * cache.filters.data[j * n_fb + k + 2] +
fft_out[k + 3] * cache.filters.data[j * n_fb + k + 3];
}
for (; k < n_fb; k++) {
sum += fft_out[k] * cache.filters.data[j * n_fb + k];
}
mel.data[j * mel.n_len + i] = std::log(sum + eps);
}
}
// Otherwise fft_out are all zero.
const double empty_sum = std::log(eps);
for (; i < mel.n_len; i += n_threads) {
for (int j = 0; j < mel.n_mel; j++) {
mel.data[j * mel.n_len + i] = empty_sum;
}
}
}
void mtmd_audio_preprocessor_parakeet::initialize() {
cache.fill_sin_cos_table(hparams.audio_n_fft);
const size_t n_fft = hparams.audio_n_fft / 2 + 1;
GGML_ASSERT(hparams.mel_filters.size() == (size_t)hparams.n_mel_bins * n_fft);
cache.filters.n_mel = hparams.n_mel_bins;
cache.filters.n_fft = n_fft;
cache.filters.data = hparams.mel_filters;
GGML_ASSERT(hparams.window.size() == (size_t)hparams.audio_window_len);
GGML_ASSERT(hparams.window.size() <= (size_t) hparams.audio_n_fft);
cache.hann_window = hparams.window;
}
bool mtmd_audio_preprocessor_parakeet::preprocess(const float * samples,
size_t n_samples_in,
std::vector<mtmd_audio_mel> & output) {
if (n_samples_in == 0) {
return false;
}
filter_params params;
params.n_mel = hparams.n_mel_bins;
params.n_fft_bins = 1 + (hparams.audio_n_fft / 2);
params.hann_window_size = hparams.audio_window_len;
params.hop_length = hparams.audio_hop_len;
params.sample_rate = hparams.audio_sample_rate;
GGML_ASSERT(!cache.sin_vals.empty());
GGML_ASSERT(!cache.cos_vals.empty());
GGML_ASSERT(!cache.filters.data.empty());
const float * window_func = cache.hann_window.data();
const int window_size = params.hann_window_size;
const int frame_size = (params.n_fft_bins - 1) * 2;
const int frame_step = params.hop_length;
// Apply preemphasis filter (high-pass): x[i] = x[i] - 0.97 * x[i-1]
std::vector<float> samples_preprocessed(samples, samples + n_samples_in);
{
const float preemph = 0.97f;
for (int i = n_samples_in - 1; i > 0; i--) {
samples_preprocessed[i] = samples_preprocessed[i] - preemph * samples_preprocessed[i - 1];
}
}
// Parakeet uses centered constant padding
const size_t pad = (size_t)(frame_size / 2);
std::vector<float> samples_padded(n_samples_in + 2 * pad, 0.0f);
std::copy(samples_preprocessed.begin(), samples_preprocessed.end(), samples_padded.begin() + pad);
mtmd_audio_mel out_full;
out_full.n_mel = params.n_mel;
out_full.n_len = (samples_padded.size() - frame_size) / frame_step + 1;
out_full.n_len_org = out_full.n_len;
out_full.data.resize(out_full.n_mel * out_full.n_len);
const int n_threads = 4;
std::vector<std::thread> workers(n_threads - 1);
for (int iw = 0; iw < n_threads - 1; ++iw) {
workers[iw] = std::thread(
worker_thread, iw + 1,
window_func,
window_size,
std::cref(samples_padded),
samples_padded.size(),
frame_size,
frame_step,
n_threads,
params.n_fft_bins,
std::cref(cache),
std::ref(out_full)
);
}
worker_thread(0,
window_func,
window_size,
samples_padded,
samples_padded.size(),
frame_size,
frame_step,
n_threads,
params.n_fft_bins,
cache,
out_full);
for (int iw = 0; iw < n_threads - 1; ++iw) {
workers[iw].join();
}
// Per-feature normalization (only on valid frames)
{
const double eps = 1e-5;
int valid_frames = n_samples_in / frame_step;
for (int j = 0; j < out_full.n_mel; j++) {
double sum = 0.0;
double sq_diff_sum = 0.0;
// Calculate Mean ONLY on valid audio frames
for (int i = 0; i < valid_frames; i++) {
sum += (double)out_full.data[j * out_full.n_len + i];
}
double mean = sum / valid_frames;
// Calculate Variance ONLY on valid audio frames
for (int i = 0; i < valid_frames; i++) {
double diff = (double)out_full.data[j * out_full.n_len + i] - mean;
sq_diff_sum += diff * diff;
}
double std_dev = std::sqrt(sq_diff_sum / (valid_frames - 1.0));
double denominator = std_dev + eps;
// Apply to ALL frames (including the padded ones)
for (int i = 0; i < out_full.n_len; i++) {
out_full.data[j * out_full.n_len + i] = (float)((out_full.data[j * out_full.n_len + i] - mean) / denominator);
}
}
}
output.push_back(std::move(out_full));
return true;
}
// mtmd_audio_preprocessor_gemma4ua
//
void mtmd_audio_preprocessor_gemma4ua::initialize() {
// no-op: no FFT or filterbank needed
}
bool mtmd_audio_preprocessor_gemma4ua::preprocess(const float * samples,
size_t n_samples,
std::vector<mtmd_audio_mel> & output) {
if (n_samples == 0) {
return false;
}
const int frame_size = hparams.n_mel_bins; // 640 samples per token @ 16 kHz = 40 ms
const int n_tokens = ((int)n_samples + frame_size - 1) / frame_size;
mtmd_audio_mel mel;
mel.n_len = n_tokens;
mel.n_len_org = n_tokens;
mel.n_mel = frame_size;
mel.data.assign((size_t)frame_size * n_tokens, 0.0f);
// Store mel-major (data[f * n_tokens + t]) so the ggml tensor loads as
// [n_tokens, frame_size] with ne[0]=n_tokens, ne[1]=frame_size.
// The graph builder transposes before RMSNorm so normalization is over frame_size.
for (int t = 0; t < n_tokens; t++) {
for (int f = 0; f < frame_size; f++) {
size_t src = (size_t)t * frame_size + f;
mel.data[(size_t)f * n_tokens + t] = (src < n_samples) ? samples[src] : 0.0f;
}
}
output.push_back(std::move(mel));
return true;
}
//
// mtmd_audio_streaming_istft implementation
//
mtmd_audio_streaming_istft::mtmd_audio_streaming_istft(int n_fft, int hop_length) :
n_fft(n_fft),
hop_length(hop_length),
n_fft_bins(n_fft / 2 + 1),
overlap_buffer(n_fft, 0.0f),
window_sum_buffer(n_fft, 0.0f),
padding_to_remove((n_fft - hop_length) / 2),
ifft_in(n_fft * 2 * 4, 0.0f), // extra space for recursive IFFT
ifft_out(n_fft * 2 * 4, 0.0f) {
GGML_ASSERT(n_fft > 0 && hop_length > 0 && hop_length <= n_fft);
cache.fill_sin_cos_table(n_fft);
cache.fill_hann_window(n_fft, true);
}
void mtmd_audio_streaming_istft::reset() {
std::fill(overlap_buffer.begin(), overlap_buffer.end(), 0.0f);
std::fill(window_sum_buffer.begin(), window_sum_buffer.end(), 0.0f);
padding_to_remove = (n_fft - hop_length) / 2;
}
std::vector<float> mtmd_audio_streaming_istft::process_frame(const float * frame_spectrum) {
std::vector<float> output(hop_length);
// copy frequencies
for (int j = 0; j < n_fft_bins; j++) {
ifft_in[j * 2 + 0] = frame_spectrum[j * 2 + 0];
ifft_in[j * 2 + 1] = frame_spectrum[j * 2 + 1];
}
// mirror negative frequencies
for (int j = 1; j < n_fft_bins - 1; j++) {
int mirror_idx = n_fft - j;
ifft_in[mirror_idx * 2 + 0] = ifft_in[j * 2 + 0];
ifft_in[mirror_idx * 2 + 1] = -ifft_in[j * 2 + 1]; // conjugate
}
ifft(cache, ifft_in.data(), n_fft, ifft_out.data());
// update window sum and overlap buffer
for (int j = 0; j < n_fft; j++) {
window_sum_buffer[j] += cache.hann_window[j] * cache.hann_window[j];
overlap_buffer[j] += ifft_out[j * 2] * cache.hann_window[j];
}
// extract hop_length samples with normalization
for (int i = 0; i < hop_length; i++) {
if (window_sum_buffer[i] > 1e-8f) {
output[i] = overlap_buffer[i] / window_sum_buffer[i];
} else {
output[i] = overlap_buffer[i];
}
}
// shift buffers left by hop_length
std::copy(overlap_buffer.begin() + hop_length, overlap_buffer.end(), overlap_buffer.begin());
std::fill(overlap_buffer.end() - hop_length, overlap_buffer.end(), 0.0f);
std::copy(window_sum_buffer.begin() + hop_length, window_sum_buffer.end(), window_sum_buffer.begin());
std::fill(window_sum_buffer.end() - hop_length, window_sum_buffer.end(), 0.0f);
// Remove padding if needed
int to_remove = std::min(padding_to_remove, (int) output.size());
padding_to_remove -= to_remove;
output.erase(output.begin(), output.begin() + to_remove);
return output;
}
std::vector<float> mtmd_audio_streaming_istft::flush() {
std::vector<float> output;
// Extract remaining samples from overlap buffer
// Continue until we've extracted all meaningful samples
int remaining = n_fft - hop_length;
while (remaining > 0) {
int chunk_size = std::min(remaining, hop_length);
for (int i = 0; i < chunk_size; i++) {
float sample;
if (window_sum_buffer[i] > 1e-8f) {
sample = overlap_buffer[i] / window_sum_buffer[i];
} else {
sample = overlap_buffer[i];
}
output.push_back(sample);
}
// Shift buffers
std::copy(overlap_buffer.begin() + chunk_size, overlap_buffer.end(), overlap_buffer.begin());
std::fill(overlap_buffer.end() - chunk_size, overlap_buffer.end(), 0.0f);
std::copy(window_sum_buffer.begin() + chunk_size, window_sum_buffer.end(), window_sum_buffer.begin());
std::fill(window_sum_buffer.end() - chunk_size, window_sum_buffer.end(), 0.0f);
remaining -= chunk_size;
}
return output;
}