From 33078bf54a15cf29000ee2bc160d3f12a66d4857 Mon Sep 17 00:00:00 2001
From: Seungha Yang <seungha@centricular.com>
Date: Tue, 20 Apr 2021 18:37:15 +0900
Subject: [PATCH] wasapi2: Implement default audio channel mask

Some capture devices might not provide channel mask value which will
result in capturing failure because of unknown channel mask in case
that device generates more than 2 channels. Although it might not
be correct, we can assume channel mask with the given number of channels.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/2177>
---
 sys/wasapi2/gstwasapi2client.cpp | 51 ++++++++++++++++++++++++++++++++++------
 1 file changed, 44 insertions(+), 7 deletions(-)

diff --git a/sys/wasapi2/gstwasapi2client.cpp b/sys/wasapi2/gstwasapi2client.cpp
index fc04a39..8b8c047 100644
--- a/sys/wasapi2/gstwasapi2client.cpp
+++ b/sys/wasapi2/gstwasapi2client.cpp
@@ -984,17 +984,36 @@ static struct
   {SPEAKER_TOP_BACK_RIGHT, GST_AUDIO_CHANNEL_POSITION_TOP_REAR_RIGHT}
 };
 
+static DWORD default_ch_masks[] = {
+  0,
+  KSAUDIO_SPEAKER_MONO,
+  /* 2ch */
+  KSAUDIO_SPEAKER_STEREO,
+  /* 2.1ch */
+  /* KSAUDIO_SPEAKER_3POINT0 ? */
+  KSAUDIO_SPEAKER_2POINT1,
+  /* 4ch */
+  /* KSAUDIO_SPEAKER_3POINT1 or KSAUDIO_SPEAKER_SURROUND ? */
+  KSAUDIO_SPEAKER_QUAD,
+  /* 5ch */
+  KSAUDIO_SPEAKER_5POINT0,
+  /* 5.1ch */
+  KSAUDIO_SPEAKER_5POINT1,
+  /* 7ch */
+  KSAUDIO_SPEAKER_7POINT0,
+  /* 7.1ch */
+  KSAUDIO_SPEAKER_7POINT1,
+};
+
 /* Parse WAVEFORMATEX to get the gstreamer channel mask, and the wasapi channel
  * positions so GstAudioRingbuffer can reorder the audio data to match the
  * gstreamer channel order. */
 static guint64
-gst_wasapi_util_waveformatex_to_channel_mask (WAVEFORMATEXTENSIBLE * format,
-    GstAudioChannelPosition ** out_position)
+gst_wasapi2_util_waveformatex_to_channel_mask (WORD nChannels,
+    DWORD dwChannelMask, GstAudioChannelPosition ** out_position)
 {
   int ii, ch;
   guint64 mask = 0;
-  WORD nChannels = format->Format.nChannels;
-  DWORD dwChannelMask = format->dwChannelMask;
   GstAudioChannelPosition *pos = NULL;
 
   pos = g_new (GstAudioChannelPosition, nChannels);
@@ -1041,7 +1060,9 @@ gst_wasapi2_util_parse_waveformatex (WAVEFORMATEXTENSIBLE * format,
     GstAudioChannelPosition ** out_positions)
 {
   const gchar *afmt;
-  guint64 channel_mask;
+  guint64 channel_mask = 0;
+  DWORD dwChannelMask = 0;
+  WORD nChannels;
 
   *out_caps = NULL;
 
@@ -1064,9 +1085,25 @@ gst_wasapi2_util_parse_waveformatex (WAVEFORMATEXTENSIBLE * format,
 
   *out_caps = gst_caps_copy (template_caps);
 
-  /* This will always return something that might be usable */
+  nChannels = format->Format.nChannels;
+  if (format->Format.wFormatTag == WAVE_FORMAT_EXTENSIBLE) {
+    dwChannelMask = format->dwChannelMask;
+  }
+
+  if (nChannels > 2 && !dwChannelMask) {
+    GST_WARNING ("Unknown channel mask value for %d channel stream",
+        format->Format.nChannels);
+    if (nChannels >= G_N_ELEMENTS (default_ch_masks)) {
+      GST_ERROR ("To may channels %d", nChannels);
+      return FALSE;
+    }
+
+    dwChannelMask = default_ch_masks[nChannels];
+  }
+
   channel_mask =
-      gst_wasapi_util_waveformatex_to_channel_mask (format, out_positions);
+      gst_wasapi2_util_waveformatex_to_channel_mask (nChannels,
+      dwChannelMask, out_positions);
 
   gst_caps_set_simple (*out_caps,
       "format", G_TYPE_STRING, afmt,
-- 
2.7.4