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
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

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/audio/wav_dump_backend.h | 51 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 51 insertions(+)
 create mode 100644 src/audio/wav_dump_backend.h

(limited to 'src/audio/wav_dump_backend.h')

diff --git a/src/audio/wav_dump_backend.h b/src/audio/wav_dump_backend.h
new file mode 100644
index 0000000..b037fd1
--- /dev/null
+++ b/src/audio/wav_dump_backend.h
@@ -0,0 +1,51 @@
+// This file is part of the 64k demo project.
+// WAV dump backend for debugging audio output to file instead of device.
+// Stripped in final build (STRIP_ALL).
+
+#if !defined(DEMO_AUDIO_WAV_DUMP_BACKEND_H)
+#define DEMO_AUDIO_WAV_DUMP_BACKEND_H
+
+#include "audio_backend.h"
+#include <stdio.h>
+#include <vector>
+
+#if !defined(STRIP_ALL)
+
+// WAV file dump backend for debugging
+// Captures audio from synth_render() and writes to .wav file
+class WavDumpBackend : public AudioBackend {
+ public:
+  WavDumpBackend();
+  ~WavDumpBackend();
+
+  // AudioBackend interface
+  void init() override;
+  void start() override;
+  void shutdown() override;
+
+  // Set output filename (call before init())
+  void set_output_file(const char* filename);
+
+  // Get total samples written
+  size_t get_samples_written() const { return samples_written_; }
+
+ private:
+  // Write WAV header with known sample count
+  void write_wav_header(FILE* file, uint32_t num_samples);
+
+  // Update WAV header with final sample count
+  void update_wav_header();
+
+  FILE* wav_file_;
+  std::vector<float> sample_buffer_;
+  size_t samples_written_;
+  const char* output_filename_;
+  bool is_active_;
+
+  static const int kSampleRate = 32000;
+  static const int kBufferSize = 1024;
+};
+
+#endif /* !defined(STRIP_ALL) */
+
+#endif /* DEMO_AUDIO_WAV_DUMP_BACKEND_H */
-- 
cgit v1.2.3