fix(bookplayer): remove fades from page playback

Apps/BookPlayer/main/Source/main.c

@@ -32,10 +32,6 @@
 #define MAX_TITLE 128
 #define MAX_AUTHOR 128
 
-// Fade-in/out applied at the start/end of each page's narration to avoid an
-// amplitude step (audible "pop") at page boundaries. In frames per channel.
-#define FADE_FRAMES 4096
-
 typedef enum {
     STATE_IDLE,
     STATE_PLAYING,
@@ -93,6 +89,10 @@ typedef struct {
     uint8_t        stream_channels;
     uint8_t        stream_bits;
 
+    // Page navigation stops the decoder task but keeps a compatible output
+    // stream open for the next page.
+    bool           keep_stream_on_stop;
+
     TaskHandle_t   playback_task_handle;
 } AppCtx;
 
@@ -116,7 +116,7 @@ static AppCtx g_ctx;
 
 /* ─── Forward Declarations ─── */
 static void update_ui(AppCtx* ctx);
-static void wait_for_playback_task_to_exit(AppCtx* ctx);
+static void wait_for_playback_task_to_exit(AppCtx* ctx, bool keep_stream_open);
 static void load_page(AppCtx* ctx, int page_index, bool start_audio);
 static void return_to_picker(AppCtx* ctx);
 static void audio_playback_task(void* arg);
@@ -266,20 +266,22 @@ static void handle_audio_finished(AppCtx* ctx) {
 }
 
 /* ─── Helper to wait for playback thread to terminate safely ─── */
-static void wait_for_playback_task_to_exit(AppCtx* ctx) {
+static void wait_for_playback_task_to_exit(AppCtx* ctx, bool keep_stream_open) {
     if (ctx->playback_task_handle != NULL) {
+        ctx->keep_stream_on_stop = keep_stream_open;
         ctx->state = STATE_IDLE;
         while (ctx->playback_task_handle != NULL) {
             tt_lvgl_unlock();
             vTaskDelay(pdMS_TO_TICKS(10));
             tt_lvgl_lock(portMAX_DELAY);
         }
+        ctx->keep_stream_on_stop = false;
     }
 }
 
 /* ─── Load Page Content (Image, Caption, Audio path) ─── */
 static void load_page(AppCtx* ctx, int page_index, bool start_audio) {
-    wait_for_playback_task_to_exit(ctx);
+    wait_for_playback_task_to_exit(ctx, true);
 
     if (page_index < 0 || page_index >= ctx->page_count) return;
     ctx->current_page = page_index;
@@ -351,7 +353,7 @@ static void load_page(AppCtx* ctx, int page_index, bool start_audio) {
 
 /* ─── Return to Book Picker Screen ─── */
 static void return_to_picker(AppCtx* ctx) {
-    wait_for_playback_task_to_exit(ctx);
+    wait_for_playback_task_to_exit(ctx, false);
     close_stream_if_open(ctx);
 
     if (ctx->manifest_root) {
@@ -419,7 +421,6 @@ static void play_mp3(AppCtx* ctx) {
     bool eof = false;
     int sample_rate = 0;
     int channels = 0;
-    size_t page_frames_written = 0;
 
     ESP_LOGI(TAG, "Starting MP3 playback via audio-stream: %s (%d bytes)", ctx->current_audio_path, file_size);
 
@@ -474,30 +475,14 @@ static void play_mp3(AppCtx* ctx) {
                 channels = info.channels;
             }
 
-            // Adjust Volume and apply a fade-in/out at the start/end of the page
+            // Adjust volume without altering the start or end of the narration.
-            // so the transition to the next page doesn't click.
             int vol = ctx->volume;
             int16_t* samples_ptr = (int16_t*)ctx->pcm_buf;
             size_t sample_count = (size_t)samples * info.channels;
-            uint8_t ch = (uint8_t)info.channels;
-            size_t bytes_per_frame = (size_t)ch * sizeof(int16_t);
-            size_t frames_in_chunk = (size_t)samples;
-            float remaining_frames = (file_size > bytes_read_total)
-                ? (float)(file_size - bytes_read_total) / (float)bytes_per_frame : 0.0f;
             for (size_t i = 0; i < sample_count; ++i) {
-                size_t frame = page_frames_written + i / ch;
-                float fade_in = (frame < FADE_FRAMES) ? (float)frame / (float)FADE_FRAMES : 1.0f;
-                float fade_out = 1.0f;
-                float remaining = remaining_frames - (float)(i / ch);
-                if (remaining < (float)FADE_FRAMES) {
-                    fade_out = (remaining > 0.0f) ? remaining / (float)FADE_FRAMES : 0.0f;
-                }
-                float gain = fade_in * fade_out;
                 int32_t scaled = (int32_t)samples_ptr[i] * vol / 100;
-                scaled = (int32_t)((float)scaled * gain);
                 samples_ptr[i] = (int16_t)scaled;
             }
-            page_frames_written += frames_in_chunk;
 
             // Write via audio_stream (resampled to native 44100 internally)
             size_t offset = 0;
@@ -536,12 +521,10 @@ static void play_mp3(AppCtx* ctx) {
 
     bool stopped_externally = (ctx->state == STATE_IDLE);
 
-    if (stopped_externally) {
+    if (stopped_externally && !ctx->keep_stream_on_stop) {
-        // User-initiated stop (prev/next, back, app close): tear the stream down.
+        // App exit and returning to the picker release the output device.
         close_stream_if_open(ctx);
     }
-    // On a natural page finish we deliberately LEAVE the stream open so the next
-    // page reuses it, instead of closing+recreating the codec (which pops).
 
     if (!stopped_externally) {
         tt_lvgl_lock(portMAX_DELAY);
@@ -621,7 +604,6 @@ static void play_wav(AppCtx* ctx) {
     ESP_LOGI(TAG, "Starting WAV via audio-stream: %s (%u Hz, %u ch)", ctx->current_audio_path, (unsigned int)header.sample_rate, (unsigned int)header.channels);
 
     size_t total_played = 0;
-    size_t page_frames_written = 0;
     bool stream_open = true;
 
     while (total_played < data_size && ctx->state != STATE_IDLE) {
@@ -643,29 +625,14 @@ static void play_wav(AppCtx* ctx) {
         size_t read_bytes = fread(ctx->audio_buf, 1, to_read, file);
         if (read_bytes == 0) break;
 
-        // Scaling Volume + fade-in/out at page boundaries to avoid a click.
+        // Adjust volume without altering the start or end of the narration.
         int vol = ctx->volume;
         int16_t* samples_ptr = (int16_t*)ctx->audio_buf;
         size_t sample_count = read_bytes / sizeof(int16_t);
-        uint8_t ch = (header.channels > 0) ? header.channels : 1;
-        size_t bytes_per_frame = (size_t)ch * sizeof(int16_t);
-        size_t frames_in_chunk = read_bytes / bytes_per_frame;
-        float remaining_frames = (data_size > total_played)
-            ? (float)(data_size - total_played) / (float)bytes_per_frame : 0.0f;
         for (size_t i = 0; i < sample_count; ++i) {
-            size_t frame = page_frames_written + i / ch;
-            float fade_in = (frame < FADE_FRAMES) ? (float)frame / (float)FADE_FRAMES : 1.0f;
-            float fade_out = 1.0f;
-            float remaining = remaining_frames - (float)(i / ch);
-            if (remaining < (float)FADE_FRAMES) {
-                fade_out = (remaining > 0.0f) ? remaining / (float)FADE_FRAMES : 0.0f;
-            }
-            float gain = fade_in * fade_out;
             int32_t scaled = (int32_t)samples_ptr[i] * vol / 100;
-            scaled = (int32_t)((float)scaled * gain);
             samples_ptr[i] = (int16_t)scaled;
         }
-        page_frames_written += frames_in_chunk;
 
         // Write via audio_stream
         size_t offset = 0;
@@ -702,12 +669,10 @@ static void play_wav(AppCtx* ctx) {
 
     bool stopped_externally = (ctx->state == STATE_IDLE);
 
-    if (stopped_externally) {
+    if (stopped_externally && !ctx->keep_stream_on_stop) {
-        // User-initiated stop (prev/next, back, app close): tear the stream down.
+        // App exit and returning to the picker release the output device.
         close_stream_if_open(ctx);
     }
-    // On a natural page finish we deliberately LEAVE the stream open so the next
-    // page reuses it, instead of closing+recreating the codec (which pops).
 
     if (!stopped_externally) {
         tt_lvgl_lock(portMAX_DELAY);
@@ -1063,7 +1028,7 @@ static void onShowApp(AppHandle app, void* data, lv_obj_t* parent) {
 }
 
 static void onHideApp(AppHandle app, void* data) {
-    wait_for_playback_task_to_exit(&g_ctx);
+    wait_for_playback_task_to_exit(&g_ctx, false);
     close_stream_if_open(&g_ctx);
 
     if (g_ctx.manifest_root) {