feat: export selection to WAV (band-limited, time-cropped)

New "Export WAV (W)" button + W key saves the current selection as a mono
WAV — the same band-limited, time-cropped audio you'd hear on playback, so
"what you hear is what you save". Self-documenting filename encodes the
time span and frequency band (rspektrum_sel_<t0>-<t1>s_<f0>-<f1>Hz.wav).

Refactor the shared filtered-region builder out of PlaySelectedRegion
(which also fixes a leak: it never freed regionSamples after
LoadSoundFromWave copies it). Make the export confirmation message persist
~3s instead of flashing for a single frame (affected PNG export too).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/audio.c

@@ -187,16 +187,21 @@ static void ApplyBandpassFilter(float* samples, int numSamples, int sampleRate,
     ApplyBandpassFilterFFT(samples, numSamples, sampleRate, freqLow, freqHigh);
 }
 
-void PlaySelectedRegion(void)
+// Build the current selection's audio: the samples in the selected time span,
+// band-limited to the selected frequency box (same processing as playback, so
+// "what you hear is what you save"). Returns a malloc'd mono float buffer the
+// caller must free, with *outNumSamples set; NULL if there's no valid region.
+static float* BuildSelectionAudio(int* outNumSamples)
 {
-    if (!app.loaded || !app.stftComputed) return;
+    if (!app.loaded || !app.stftComputed) return NULL;
 
     int startSample = (int)(app.sel.timeStart * app.signal.numSamples);
     int endSample = (int)(app.sel.timeEnd * app.signal.numSamples);
     int numSamples = endSample - startSample;
-    if (numSamples <= 0 || startSample < 0 || endSample > app.signal.numSamples) return;
+    if (numSamples <= 0 || startSample < 0 || endSample > app.signal.numSamples) return NULL;
 
     float* regionSamples = (float*)malloc(numSamples * sizeof(float));
+    if (!regionSamples) return NULL;
     memcpy(regionSamples, app.signal.samples + startSample, numSamples * sizeof(float));
 
     float maxFreq = (float)app.signal.sampleRate / 2.0f;
@@ -207,13 +212,53 @@ void PlaySelectedRegion(void)
         ApplyBandpassFilter(regionSamples, numSamples, app.signal.sampleRate, freqLow, freqHigh);
     }
 
+    *outNumSamples = numSamples;
+    return regionSamples;
+}
+
+void PlaySelectedRegion(void)
+{
+    int numSamples = 0;
+    float* regionSamples = BuildSelectionAudio(&numSamples);
+    if (!regionSamples) return;
+
     if (AudioPlaybackSound.frameCount != 0) UnloadSound(AudioPlaybackSound);
 
     Wave wave = { .data = regionSamples, .frameCount = (unsigned int)numSamples,
                   .sampleRate = (unsigned int)app.signal.sampleRate, .sampleSize = 32, .channels = 1 };
-    AudioPlaybackSound = LoadSoundFromWave(wave);
+    AudioPlaybackSound = LoadSoundFromWave(wave);  // copies the samples
     PlaySound(AudioPlaybackSound);
-    TraceLog(LOG_INFO, "Playing: %.2f-%.2f sec, %.0f-%.0f Hz",
-             (float)startSample / app.signal.sampleRate, (float)endSample / app.signal.sampleRate, freqLow, freqHigh);
+    free(regionSamples);
+}
+
+void ExportSelectionWAV(const char* dirPath)
+{
+    int numSamples = 0;
+    float* samples = BuildSelectionAudio(&numSamples);
+    if (!samples) {
+        snprintf(app.exportMessage, sizeof(app.exportMessage), "No region to export");
+        app.exportMessageTimer = 3.0f;
+        return;
+    }
+
+    float maxFreq = (float)app.signal.sampleRate / 2.0f;
+    float t0 = app.sel.timeStart * app.signal.duration;
+    float t1 = app.sel.timeEnd * app.signal.duration;
+    float f0 = app.sel.freqStart * maxFreq;
+    float f1 = app.sel.freqEnd * maxFreq;
+
+    char path[4608];
+    snprintf(path, sizeof(path), "%s/rspektrum_sel_%.0f-%.0fs_%.0f-%.0fHz.wav",
+             dirPath, t0, t1, f0, f1);
+
+    Wave wave = { .data = samples, .frameCount = (unsigned int)numSamples,
+                  .sampleRate = (unsigned int)app.signal.sampleRate, .sampleSize = 32, .channels = 1 };
+    if (ExportWave(wave, path))
+        snprintf(app.exportMessage, sizeof(app.exportMessage), "Saved WAV: %.40s", path);
+    else
+        snprintf(app.exportMessage, sizeof(app.exportMessage), "WAV export failed");
+    app.exportMessageTimer = 3.0f;
+
+    free(samples);
 }
 

src/audio.h

@@ -12,4 +12,8 @@ void FreeSignal(AudioSignal* signal);
 // Play the current time/frequency selection (applies an FFT bandpass filter).
 void PlaySelectedRegion(void);
 
+// Save the current selection (band-limited, time-cropped — same processing as
+// playback) as a mono WAV in dirPath. Reports the result via app.exportMessage.
+void ExportSelectionWAV(const char* dirPath);
+
 #endif // AUDIO_H

src/spectrogram.c

@@ -154,6 +154,7 @@ static void ActionToggleScope(void)    { app.showScope = !app.showScope; }
 static void ActionToggleAbout(void)    { app.showAbout = !app.showAbout; }
 static void ActionToggleFullscreen(void){ ToggleFullscreen(); }
 static void ActionExport(void)         { ExportPNG(&app, app.exportDir); }
+static void ActionExportWav(void)      { ExportSelectionWAV(app.exportDir); }
 
 static void ActionResetView(void)
 {
@@ -177,6 +178,7 @@ static const KeyBinding KEYMAP[] = {
     { KEY_HOME,  KEYGATE_MODAL | KEYGATE_LOADED,ActionResetView,       "Home",  "reset view (fit all)" },
     { KEY_END,   KEYGATE_MODAL | KEYGATE_LOADED,ActionZoomToStart,     "End",   "zoom to start" },
     { KEY_E,     KEYGATE_MODAL | KEYGATE_STFT,  ActionExport,          "E",     "export PNG" },
+    { KEY_W,     KEYGATE_MODAL | KEYGATE_STFT,  ActionExportWav,       "W",     "export selection WAV" },
     // Order-sensitive: handled inline (see main loop), listed here for the overlay.
     { KEY_SPACE, KEYGATE_NONE,                  NULL,                  "Space", "play / stop selection" },
     { KEY_ESCAPE,KEYGATE_NONE,                  NULL,                  "Esc",   "clear selection / close dialog" },
@@ -1062,8 +1064,11 @@ int main(int argc, char* argv[])
             DrawText(app.exportMessage, boxX + (boxW - msgW) / 2, boxY + 10, 20, WHITE);
         }
 
-        // Reset export message after one frame display
-        app.exportMessage[0] = '\0';
+        // Hold the export message for a few seconds, then clear it.
+        if (app.exportMessageTimer > 0.0f) {
+            app.exportMessageTimer -= GetFrameTime();
+            if (app.exportMessageTimer <= 0.0f) app.exportMessage[0] = '\0';
+        }
 
         EndDrawing();
     }

src/spectrogram_types.h

@@ -136,6 +136,7 @@ typedef struct {
     float exportScale;
     char exportDir[4096];
     char exportMessage[256];
+    float exportMessageTimer;  // seconds the export message stays on screen
 
     // Visible viewport (time + frequency) and in-progress pan state.
     Viewport view;

src/ui.c

@@ -323,6 +323,7 @@ void ExportPNG(const SpectrogramApp* spa, const char* dirPath)
     } else {
         snprintf((char*)spa->exportMessage, sizeof(spa->exportMessage), "Export failed");
     }
+    ((SpectrogramApp*)spa)->exportMessageTimer = 3.0f;
 
     RL_FREE(region.data);
 }
@@ -484,6 +485,15 @@ void DrawSidebar(void)
         DrawTextScaled("Export PNG (E)", exportButton.x + 10 * scale, exportButton.y + 7 * scale, 14, WHITE);
         y += 35 * scale;
 
+        // Export selection audio (band-limited, time-cropped) as a WAV
+        Rectangle wavButton = { x, y, sidebarWidth - 10 * scale, 30 * scale };
+        if (Clicked(wavButton)) {
+            ExportSelectionWAV(app.exportDir);
+        }
+        DrawPanelBox(wavButton, (Color){ 40, 60, 80, 255 }, CYAN);
+        DrawTextScaled("Export WAV (W)", wavButton.x + 10 * scale, wavButton.y + 7 * scale, 14, WHITE);
+        y += 35 * scale;
+
         // Export scale slider
         DrawTextScaled(TextFormat("Export Scale: %.1fx", app.exportScale), x, y, 12, LIGHTGRAY); y += 18 * scale;
         Rectangle scaleSlider = { x, y, sidebarWidth - 10 * scale, 14 * scale };