Do not set audio device for desktop capture if audio loopback is unsupported

Desktop audio capture requires loopback device. If creation of the
loopback device fails, it aborts the screen capture too.

Chromium does not support audio loopback on Linux and macOS:
https://crbug.com/223639

This is still the case in Chrome 88.
The fix is based on: https://codereview.chromium.org/24153018

Change-Id: Ifb13bce3b79193203c0bf52e1f2a1b3936e017c7
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>

2 files changed, 12 insertions, 3 deletions

diff --git a/src/core/media_capture_devices_dispatcher.cpp b/src/core/media_capture_devices_dispatcher.cpp
index 693cfa2e3..ac74c509c 100644
--- a/src/core/media_capture_devices_dispatcher.cpp
+++ b/src/core/media_capture_devices_dispatcher.cpp
@@ -272,7 +272,8 @@ void MediaCaptureDevicesDispatcher::handleMediaAccessPermissionResponse(content:
                 break;
             }
         } else if (desktopVideoRequested) {
-            getDevicesForDesktopCapture(&devices, getDefaultScreenId(), desktopAudioRequested,
+            bool captureAudio = desktopAudioRequested && m_loopbackAudioSupported;
+            getDevicesForDesktopCapture(&devices, getDefaultScreenId(), captureAudio,
                                         request.video_type, request.audio_type);
         }
     }
@@ -309,6 +310,10 @@ MediaCaptureDevicesDispatcher::MediaCaptureDevicesDispatcher()
     // content::NOTIFICATION_WEB_CONTENTS_DESTROYED, and that will result in
     // possible use after free.
     DCHECK_CURRENTLY_ON(BrowserThread::UI);
+#if defined(OS_WIN)
+    // Currently loopback audio capture is supported only on Windows.
+    m_loopbackAudioSupported = true;
+#endif
     m_notificationsRegistrar.Add(this, content::NOTIFICATION_WEB_CONTENTS_DESTROYED,
                                  content::NotificationService::AllSources());
 }
@@ -383,9 +388,11 @@ void MediaCaptureDevicesDispatcher::processDesktopCaptureAccessRequest(content::
     }
 
     // Audio is only supported for screen capture streams.
-    bool capture_audio = (mediaId.type == content::DesktopMediaID::TYPE_SCREEN && request.audio_type == MediaStreamType::GUM_DESKTOP_AUDIO_CAPTURE);
+    bool audioRequested = request.audio_type == MediaStreamType::GUM_DESKTOP_AUDIO_CAPTURE;
+    bool audioSupported = (mediaId.type == content::DesktopMediaID::TYPE_SCREEN && m_loopbackAudioSupported);
+    bool captureAudio = (audioRequested && audioSupported);
 
-    getDevicesForDesktopCapture(&devices, mediaId, capture_audio, request.video_type, request.audio_type);
+    getDevicesForDesktopCapture(&devices, mediaId, captureAudio, request.video_type, request.audio_type);
 
     if (devices.empty())
         std::move(callback).Run(devices, MediaStreamRequestResult::INVALID_STATE,
diff --git a/src/core/media_capture_devices_dispatcher.h b/src/core/media_capture_devices_dispatcher.h
index 6a67a53e9..17cb5d5c9 100644
--- a/src/core/media_capture_devices_dispatcher.h
+++ b/src/core/media_capture_devices_dispatcher.h
@@ -127,6 +127,8 @@ private:
 
     content::NotificationRegistrar m_notificationsRegistrar;
 
+    bool m_loopbackAudioSupported = false;
+
     DISALLOW_COPY_AND_ASSIGN(MediaCaptureDevicesDispatcher);
 };