PulseAudio: correct volume reporting from PA to VLC (fix #6759)

The proper reciprocal formula to that of VLC to PA conversion must be
used. Otherwise, we get an inconsistent value in the "volume" variable.
(cherry picked from commit a89517ca4be10847d17db539ed6acf5302fb65dd)

modules/audio_output/pulse.c

@@ -473,15 +473,16 @@ static void sink_input_info_cb(pa_context *ctx, const pa_sink_input_info *i,
 {
     audio_output_t *aout = userdata;
     aout_sys_t *sys = aout->sys;
-    float volume;
 
     if (eol)
         return;
     (void) ctx;
 
-    sys->cvolume = i->volume;
-    volume = pa_cvolume_max(&i->volume) / (float)PA_VOLUME_NORM;
-    aout_VolumeHardSet(aout, volume, i->mute);
+    sys->cvolume = i->volume; /* cache volume for balance preservation */
+
+    pa_volume_t volume = pa_cvolume_max(&i->volume);
+    volume = pa_sw_volume_divide(volume, sys->base_volume);
+    aout_VolumeHardSet(aout, (float)volume / PA_VOLUME_NORM, i->mute);
 }
 
 
@@ -605,18 +606,17 @@ static int VolumeSet(audio_output_t *aout, float vol, bool mute)
     pa_operation *op;
     uint32_t idx = pa_stream_get_index(sys->stream);
 
-    pa_cvolume cvolume = sys->cvolume;
-    pa_volume_t volume = sys->base_volume;
-
-    pa_cvolume_scale(&cvolume, PA_VOLUME_NORM); /* preserve balance */
-
     /* VLC provides the software volume so convert directly to PulseAudio
      * software volume, pa_volume_t. This is not a linear amplification factor
      * so do not use PulseAudio linear amplification! */
     vol *= PA_VOLUME_NORM;
     if (unlikely(vol >= PA_VOLUME_MAX))
         vol = PA_VOLUME_MAX;
-    volume = pa_sw_volume_multiply(volume, lround(vol));
+    pa_volume_t volume = pa_sw_volume_multiply(lround(vol), sys->base_volume);
+
+    /* Preserve the balance (VLC does not support it). */
+    pa_cvolume cvolume = sys->cvolume;
+    pa_cvolume_scale(&cvolume, PA_VOLUME_NORM);
     pa_sw_cvolume_multiply_scalar(&cvolume, &cvolume, volume);
 
     assert(pa_cvolume_valid(&cvolume));