wasapi: don't up-mix

modules/audio_output/wasapi.c

@@ -367,15 +367,14 @@ static void vlc_ToWave(WAVEFORMATEXTENSIBLE *restrict wf,
             wf->dwChannelMask |= chans_in[i];
 }
 
-static int vlc_FromWave(const WAVEFORMATEX *restrict wf,
+static int vlc_FromWave(WAVEFORMATEX *restrict wf,
                         audio_sample_format_t *restrict audio)
 {
     audio->i_rate = wf->nSamplesPerSec;
-    audio->i_physical_channels = 0;
 
     if (wf->wFormatTag == WAVE_FORMAT_EXTENSIBLE)
     {
-        const WAVEFORMATEXTENSIBLE *wfe = (void *)wf;
+        WAVEFORMATEXTENSIBLE *wfe = (void *)wf;
 
         if (IsEqualIID(&wfe->SubFormat, &KSDATAFORMAT_SUBTYPE_IEEE_FLOAT))
         {
@@ -409,18 +408,32 @@ static int vlc_FromWave(const WAVEFORMATEX *restrict wf,
         if (wfe->Samples.wValidBitsPerSample != wf->wBitsPerSample)
             return -1;
 
-        for (unsigned i = 0; chans_in[i]; i++)
-            if (wfe->dwChannelMask & chans_in[i])
-                audio->i_physical_channels |= pi_vlc_chan_order_wg4[i];
+        if (wf->nChannels <= audio->i_channels)
+        {
+            /* VLC will downmix to match the modified format */
+            audio->i_physical_channels = 0;
+            for (unsigned i = 0; chans_in[i]; i++)
+                if (wfe->dwChannelMask & chans_in[i])
+                    audio->i_physical_channels |= pi_vlc_chan_order_wg4[i];
+            audio->i_original_channels = audio->i_physical_channels;
+            aout_FormatPrepare (audio);
+            if (wf->nChannels != audio->i_channels)
+                return -1;
+        }
+        else
+        {
+            /* Force the modified format channels to VLC one in order to avoid
+             * a useless up-mixing */
+            wfe->dwChannelMask = 0;
+            for (unsigned i = 0; pi_vlc_chan_order_wg4[i]; i++)
+                if (audio->i_physical_channels & pi_vlc_chan_order_wg4[i])
+                    wfe->dwChannelMask |= chans_in[i];
+            wf->nChannels = audio->i_channels;
+        }
     }
     else
         return -1;
 
-    audio->i_original_channels = audio->i_physical_channels;
-    aout_FormatPrepare (audio);
-
-    if (wf->nChannels != audio->i_channels)
-        return -1;
     return 0;
 }