fix stft detect to support torchaudio.transforms.MelSpectrogram

tools/pnnx/src/CMakeLists.txt

@@ -433,6 +433,7 @@ set(pnnx_pass_ncnn_SRCS
     pass_ncnn/expand_expression.cpp
     pass_ncnn/fuse_convert_shufflechannel_slice.cpp
     pass_ncnn/fuse_convert_rotaryembed.cpp
+    pass_ncnn/fuse_convert_stft.cpp
     pass_ncnn/insert_split.cpp
     pass_ncnn/chain_multi_output.cpp
     pass_ncnn/solve_batch_index.cpp

tools/pnnx/src/pass_ncnn.cpp

@@ -24,6 +24,7 @@
 #include "pass_ncnn/expand_expression.h"
 #include "pass_ncnn/fuse_convert_shufflechannel_slice.h"
 #include "pass_ncnn/fuse_convert_rotaryembed.h"
+#include "pass_ncnn/fuse_convert_stft.h"
 #include "pass_ncnn/insert_split.h"
 #include "pass_ncnn/chain_multi_output.h"
 #include "pass_ncnn/solve_batch_index.h"
@@ -81,6 +82,7 @@ void pass_ncnn(Graph& g, const std::vector<std::string>& module_operators)
     attribute_unpooling(g);
 
     ncnn::fuse_convert_rotaryembed(g);
+    ncnn::fuse_convert_stft(g);
 
     ncnn::expand_expression(g);
 

tools/pnnx/src/pass_ncnn/fuse_convert_stft.cpp

@@ -0,0 +1,124 @@
+// Copyright 2026 Futz12 <pchar.cn>
+// SPDX-License-Identifier: BSD-3-Clause
+
+#include "fuse_convert_stft.h"
+
+#include "pass_level2.h"
+
+namespace pnnx {
+
+namespace ncnn {
+
+static bool NearlyEqual(float a, float b, float epsilon)
+{
+    if (a == b)
+        return true;
+
+    float diff = (float)fabs(a - b);
+    if (diff <= epsilon)
+        return true;
+
+    // relative error
+    return diff < epsilon * std::max(fabs(a), fabs(b));
+}
+
+static int detect_window_type(const std::vector<float>& window_data)
+{
+    const int winlen = (int)window_data.size();
+
+    bool is_one = true;
+    bool is_hann = true;
+    bool is_hamming = true;
+    for (int i = 0; i < winlen; i++)
+    {
+        if (!NearlyEqual(window_data[i], 1.f, 0.001))
+            is_one = false;
+
+        if (!NearlyEqual(window_data[i], 0.5f * (1 - cos(2 * 3.14159265358979323846 * i / winlen)), 0.001))
+            is_hann = false;
+
+        if (!NearlyEqual(window_data[i], 0.54f - 0.46f * cos(2 * 3.14159265358979323846 * i / winlen), 0.001))
+            is_hamming = false;
+    }
+
+    if (is_one)
+        return 0;
+    if (is_hann)
+        return 1;
+    if (is_hamming)
+        return 2;
+
+    return -1;
+}
+
+class fuse_stft_pass : public GraphRewriterPass
+{
+public:
+    const char* match_pattern_graph() const
+    {
+        return R"PNNXIR(7767517
+6 5
+pnnx.Input              input       0 1 input
+pnnx.Attribute          op_0        0 1 window @data
+torch.stft              op_1        2 1 input window a center=%center hop_length=%hop_length n_fft=%n_fft normalized=%normalized onesided=%onesided pad_mode=%pad_mode return_complex=True win_length=%win_length
+Tensor.reshape          op_2        1 1 a b shape=(1,1,%freq,%time)
+pnnx.Expression         op_3        1 1 b out expr=pow(abs(@0),2.0)
+pnnx.Output             output      1 0 out
+)PNNXIR";
+    }
+
+    const char* type_str() const
+    {
+        return "Spectrogram";
+    }
+
+    const char* name_str() const
+    {
+        return "stft";
+    }
+
+    bool match(const std::map<std::string, Parameter>& /*captured_params*/, const std::map<std::string, Attribute>& captured_attrs) const
+    {
+        const std::vector<float> window_data = captured_attrs.at("op_0.data").get_float32_data();
+        const int window_type = detect_window_type(window_data);
+        return window_type != -1;
+    }
+
+    void write(Operator* op, const std::map<std::string, Parameter>& captured_params, const std::map<std::string, Attribute>& captured_attrs) const
+    {
+        const std::vector<float> window_data = captured_attrs.at("op_0.data").get_float32_data();
+        const int window_type = detect_window_type(window_data);
+
+        const std::string& pad_mode = captured_params.at("pad_mode").s;
+        int pad_type = 2;
+        if (pad_mode == "constant")
+            pad_type = 0;
+        if (pad_mode == "replicate")
+            pad_type = 1;
+        if (pad_mode == "reflect")
+            pad_type = 2;
+        const int onesided = captured_params.at("onesided").type == 1 && captured_params.at("onesided").b == false ? 0 : 1;
+
+        op->params["0"] = captured_params.at("n_fft");
+        op->params["1"] = 2; // power
+        op->params["2"] = captured_params.at("hop_length");
+        op->params["3"] = captured_params.at("win_length");
+        op->params["4"] = window_type;
+        op->params["5"] = captured_params.at("center").type == 1 && captured_params.at("center").b ? 1 : 0;
+        op->params["6"] = pad_type;
+        op->params["7"] = captured_params.at("normalized").type == 1 && captured_params.at("normalized").b ? 1 : 0;
+        op->params["8"] = onesided;
+    }
+};
+
+void fuse_convert_stft(Graph& graph)
+{
+    fuse_stft_pass a;
+    int opindex = 0;
+
+    pnnx_graph_rewrite(graph, &a, opindex);
+}
+
+} // namespace ncnn
+
+} // namespace pnnx

tools/pnnx/src/pass_ncnn/fuse_convert_stft.h

@@ -0,0 +1,14 @@
+// Copyright 2026 Futz12 <pchar.cn>
+// SPDX-License-Identifier: BSD-3-Clause
+
+#include "ir.h"
+
+namespace pnnx {
+
+namespace ncnn {
+
+void fuse_convert_stft(Graph& graph);
+
+} // namespace ncnn
+
+} // namespace pnnx