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fix(receiver): release audio device while idle #172

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96 changes: 67 additions & 29 deletions TargetBridge-Receiver/TBReceiverC/src/main.c
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Original file line number Diff line number Diff line change
Expand Up @@ -108,6 +108,7 @@ struct app {
int input_tap_consumes_events;

SDL_AudioDeviceID audio_device;
uint64_t audio_retry_after_ms;

uint8_t audio_buf[AUDIO_BUF_CAP];
int audio_buf_head;
Expand Down Expand Up @@ -979,6 +980,62 @@ static void audio_callback(void *userdata, Uint8 *stream, int len) {
}
}

/* Keep the output device closed while Receiver is waiting for a Sender. On
* macOS an open SDL output device is enough for coreaudiod to assert
* PreventUserIdleSystemSleep, even when the callback only produces silence.
* Opening lazily also means sessions with audio disabled never touch the
* system output device. */
static int tb_audio_open_for_frame(struct app *a) {
if (!a) return 0;
if (a->audio_device != 0) return 1;

uint64_t now = now_ms();
if (now < a->audio_retry_after_ms) return 0;

SDL_AudioSpec spec;
SDL_zero(spec);
spec.freq = 48000;
spec.format = AUDIO_S16LSB;
spec.channels = 2;
spec.samples = 1024;
spec.callback = audio_callback;
spec.userdata = a;

SDL_AudioSpec obtained;
SDL_zero(obtained);
a->audio_device = SDL_OpenAudioDevice(NULL, 0, &spec, &obtained, 0);
if (a->audio_device == 0) {
/* Audio packets arrive frequently. Avoid retrying (and logging) for
* every packet if the output device is temporarily unavailable. */
a->audio_retry_after_ms = now + 5000;
fprintf(stderr, "[main] warning: SDL_OpenAudioDevice failed: %s; retrying in 5s\n",
SDL_GetError());
return 0;
}

a->audio_retry_after_ms = 0;
fprintf(stderr,
"[main] SDL audio device opened on first audio frame: "
"48000Hz stereo 16-bit PCM (obtained %d samples)\n",
obtained.samples);
return 1;
}

static void tb_audio_close_for_idle(struct app *a) {
if (!a) return;

if (a->audio_device != 0) {
SDL_CloseAudioDevice(a->audio_device);
a->audio_device = 0;
fprintf(stderr, "[main] SDL audio device closed for idle Receiver\n");
}

a->audio_buf_head = 0;
a->audio_buf_tail = 0;
a->audio_buf_size = 0;
a->audio_retry_after_ms = 0;
}

/* Drive the receiver's master output volume knob (with the system volume HUD).
* level is clamped to 0.0..1.0. Sets the default output device's scalar volume,
* preferring the master element and falling back to per-channel when a device
Expand Down Expand Up @@ -1157,7 +1214,10 @@ static void on_packet(uint8_t type, const uint8_t *payload, size_t len, void *ud
}
break;
case TB_PKT_AUDIO_FRAME:
if (a->audio_device != 0) {
{
int opened_for_frame = a->audio_device == 0;
if (!tb_audio_open_for_frame(a)) break;

SDL_LockAudioDevice(a->audio_device);

// Limit audio backlog to 150ms (150 * 192 = 28800 bytes) to cushion
Expand All @@ -1183,6 +1243,10 @@ static void on_packet(uint8_t type, const uint8_t *payload, size_t len, void *ud
}

SDL_UnlockAudioDevice(a->audio_device);

/* SDL opens devices paused. Queue the first packet before
* starting playback so the callback does not begin with silence. */
if (opened_for_frame) SDL_PauseAudioDevice(a->audio_device, 0);
}
break;
case TB_PKT_INPUT_EVENT:
Expand Down Expand Up @@ -1813,13 +1877,7 @@ static void close_client(struct app *a) {
tb_parser_free(&a->parser);
tb_parser_init(&a->parser, on_packet, a);
tb_dec_reset(a->dec); /* fresh decoder for next session */
if (a->audio_device != 0) {
SDL_LockAudioDevice(a->audio_device);
a->audio_buf_head = 0;
a->audio_buf_tail = 0;
a->audio_buf_size = 0;
SDL_UnlockAudioDevice(a->audio_device);
}
tb_audio_close_for_idle(a);
fprintf(stderr, "[main] client disconnected\n");
}

Expand Down Expand Up @@ -1931,24 +1989,6 @@ int main(int argc, char **argv) {
a.disp = tb_disp_create(fullscreen);
if (!a.disp) { fprintf(stderr, "tb_disp_create failed\n"); return 1; }

/* Open SDL Audio Device */
SDL_AudioSpec spec;
SDL_zero(spec);
spec.freq = 48000;
spec.format = AUDIO_S16LSB; // 16-bit signed, little-endian PCM
spec.channels = 2; // Stereo
spec.samples = 1024; // Buffer size (approx 21.3ms)
spec.callback = audio_callback;
spec.userdata = &a;
SDL_AudioSpec obtained;
a.audio_device = SDL_OpenAudioDevice(NULL, 0, &spec, &obtained, 0);
if (a.audio_device != 0) {
SDL_PauseAudioDevice(a.audio_device, 0); // Start playing (unpaused)
fprintf(stderr, "[main] SDL audio device opened: 48000Hz stereo 16-bit PCM (obtained %d samples)\n", obtained.samples);
} else {
fprintf(stderr, "[main] warning: SDL_OpenAudioDevice failed: %s\n", SDL_GetError());
}

struct tb_display_info boot_info;
if (tb_disp_get_info(a.disp, &boot_info) == 0) {
snprintf(a.panel_text, sizeof(a.panel_text), "%u x %u px (%s)",
Expand Down Expand Up @@ -2181,9 +2221,7 @@ int main(int argc, char **argv) {
bonjour_deinit(&a);
tb_parser_free(&a.parser);
tb_dec_destroy(a.dec);
if (a.audio_device != 0) {
SDL_CloseAudioDevice(a.audio_device);
}
tb_audio_close_for_idle(&a);
tb_disp_destroy(a.disp);
fprintf(stderr, "[main] bye\n");
return 0;
Expand Down
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