From 18c553b0aaa9a574a2a40e5499120ac8a802b735 Mon Sep 17 00:00:00 2001
From: skal <pascal.massimino@gmail.com>
Date: Wed, 4 Feb 2026 13:55:45 +0100
Subject: feat(audio): Add WAV dump backend for debugging audio output
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Implemented WavDumpBackend that renders audio to .wav file instead of
playing on audio device. Useful for debugging audio synthesis, tempo
scaling, and tracker output without needing real-time playback.

New Files:
- src/audio/wav_dump_backend.h: WAV dump backend interface
- src/audio/wav_dump_backend.cc: Implementation with WAV file writing

Features:
- Command line option: --dump_wav [filename]
- Default output: audio_dump.wav
- Format: 16-bit PCM, mono, 32kHz
- Duration: 60 seconds (configurable in code)
- Progress indicator during rendering
- Properly writes WAV header (RIFF format)

Integration (src/main.cc):
- Added --dump_wav command line parsing
- Optional filename parameter
- Sets WavDumpBackend before audio_init()
- Skips main loop in WAV dump mode (just render and exit)
- Zero size impact (all code under !STRIP_ALL)

Usage:
  ./demo64k --dump_wav                    # outputs audio_dump.wav
  ./demo64k --dump_wav my_audio.wav       # custom filename

Technical Details:
- Uses AudioBackend interface (from Task #51)
- Calls synth_render() in loop to capture audio
- Converts float samples to int16_t for WAV format
- Updates WAV header with final sample count on shutdown
- Renders 60s worth of audio (1,920,000 samples @ 32kHz)

Test Results:
✓ All 16 tests passing (100%)
✓ Successfully renders 3.7 MB WAV file
✓ File verified as valid RIFF WAVE format
✓ Playback in audio players confirmed

Perfect for:
- Debugging tempo scaling behavior
- Verifying tracker pattern timing
- Analyzing audio output offline
- Creating reference audio for tests

handoff(Claude): WAV dump debugging feature complete

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>
---
 src/main.cc | 34 +++++++++++++++++++++++++++++++++-
 1 file changed, 33 insertions(+), 1 deletion(-)

(limited to 'src/main.cc')

diff --git a/src/main.cc b/src/main.cc
index 3d05822..12f4b3d 100644
--- a/src/main.cc
+++ b/src/main.cc
@@ -7,6 +7,9 @@
 #include "audio/gen.h"
 #include "audio/synth.h"
 #include "audio/tracker.h"
+#if !defined(STRIP_ALL)
+#include "audio/wav_dump_backend.h"
+#endif
 #include "generated/assets.h" // Include generated asset header
 #include "gpu/gpu.h"
 #include "platform.h"
@@ -51,6 +54,8 @@ int main(int argc, char** argv) {
   float seek_time = 0.0f;
   int width = 1280;
   int height = 720;
+  bool dump_wav = false;
+  const char* wav_output_file = "audio_dump.wav";
 
 #if !defined(STRIP_ALL)
   for (int i = 1; i < argc; ++i) {
@@ -68,6 +73,12 @@ int main(int argc, char** argv) {
       }
     } else if (strcmp(argv[i], "--debug") == 0) {
       Renderer3D::SetDebugEnabled(true);
+    } else if (strcmp(argv[i], "--dump_wav") == 0) {
+      dump_wav = true;
+      // Optional: allow specifying output filename
+      if (i + 1 < argc && argv[i + 1][0] != '-') {
+        wav_output_file = argv[++i];
+      }
     }
   }
 #else
@@ -78,6 +89,17 @@ int main(int argc, char** argv) {
 
   platform_state = platform_init(fullscreen_enabled, width, height);
   gpu_init(&platform_state);
+
+#if !defined(STRIP_ALL)
+  // Set WAV dump backend if requested
+  WavDumpBackend wav_backend;
+  if (dump_wav) {
+    wav_backend.set_output_file(wav_output_file);
+    audio_set_backend(&wav_backend);
+    printf("WAV dump mode enabled: %s\n", wav_output_file);
+  }
+#endif
+
   audio_init();
   synth_init();
   tracker_init();
@@ -178,9 +200,19 @@ int main(int argc, char** argv) {
   }
 #endif /* !defined(STRIP_ALL) */
 
-  // Start real audio
+  // Start audio (or render to WAV file)
   audio_start();
 
+#if !defined(STRIP_ALL)
+  // In WAV dump mode, audio_start() renders everything and we can exit
+  if (dump_wav) {
+    audio_shutdown();
+    gpu_shutdown();
+    platform_shutdown(&platform_state);
+    return 0;
+  }
+#endif
+
   int last_width = platform_state.width;
   int last_height = platform_state.height;
 
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