auhal: implement pause by output silence instead of stopping output

Stopping and restarting the audio unit or device might take a
considerable amount of time. This leads to flushes, and
the user notice a delay for resuming audio.

Auhal does not have a better API for pause, so lets only play silence
for now. This fixes resume delays with analog mode, and might improve
delays for digital mode (through they are still occuring from
time to time here).

close #9536

modules/audio_output/auhal.c

@@ -112,6 +112,7 @@ struct aout_sys_t
 
     float                       f_volume;
     bool                        b_mute;
+    bool                        b_paused;
 
     vlc_mutex_t                 lock;
     vlc_cond_t                  cond;
@@ -190,6 +191,7 @@ static int Open(vlc_object_t *obj)
     p_sys->b_digital = false;
     p_sys->b_ignore_streams_changed_callback = false;
     p_sys->b_selected_dev_is_default = false;
+    p_sys->b_paused = false;
 
     p_aout->sys = p_sys;
     p_aout->start = Start;
@@ -311,6 +313,7 @@ static int Start(audio_output_t *p_aout, audio_sample_format_t *restrict fmt)
     p_sys->b_revert = false;
     p_sys->b_changed_mixing = false;
     p_sys->i_bytes_per_sample = 0;
+    p_sys->b_paused = false;
 
     vlc_mutex_lock(&p_sys->var_lock);
     p_sys->i_selected_dev = p_sys->i_new_selected_dev;
@@ -1367,17 +1370,9 @@ static void Pause(audio_output_t *p_aout, bool pause, mtime_t date)
     struct aout_sys_t * p_sys = p_aout->sys;
     VLC_UNUSED(date);
 
-    if (p_aout->sys->b_digital) {
-        if (pause)
-            AudioDeviceStop(p_sys->i_selected_dev, p_sys->i_procID);
-        else
-            AudioDeviceStart(p_sys->i_selected_dev, p_sys->i_procID);
-    } else {
-        if (pause)
-            AudioOutputUnitStop(p_sys->au_unit);
-        else
-            AudioOutputUnitStart(p_sys->au_unit);
-    }
+    vlc_mutex_lock(&p_sys->lock);
+    p_sys->b_paused = pause;
+    vlc_mutex_unlock(&p_sys->lock);
 }
 
 static void Flush(audio_output_t *p_aout, bool wait)
@@ -1444,7 +1439,7 @@ static OSStatus RenderCallbackAnalog(vlc_object_t *p_obj,
     Float32 *buffer = TPCircularBufferTail(&p_sys->circular_buffer, &availableBytes);
 
     /* check if we have enough data */
-    if (!availableBytes) {
+    if (!availableBytes || p_sys->b_paused) {
         /* return an empty buffer so silence is played until we have data */
         memset(targetBuffer, 0, ioData->mBuffers[0].mDataByteSize);
     } else {
@@ -1490,7 +1485,7 @@ static OSStatus RenderCallbackSPDIF(AudioDeviceID inDevice,
     char *buffer = TPCircularBufferTail(&p_sys->circular_buffer, &availableBytes);
 
     /* check if we have enough data */
-    if (!availableBytes) {
+    if (!availableBytes || p_sys->b_paused) {
         /* return an empty buffer so silence is played until we have data */
         memset(targetBuffer, 0, outOutputData->mBuffers[p_sys->i_stream_index].mDataByteSize);
     } else {