[camera_windows] Set device media type for video preview explicitly (flutter#7447)

Fixes preview aspect ratio on Windows on some webcams (See flutter/flutter#122966).

Before (main branch 7c1a05c):

![image](https://github.com/user-attachments/assets/cca93da9-dd94-486e-930f-5c5aa73922a9)

After:

![image](https://github.com/user-attachments/assets/05c5c460-21ed-40d8-93eb-1e75da7c929c)

Author: dasyad00

packages/camera/camera_windows/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 0.2.6+1
+
+* Fixes black bars on camera preview [#122966](https://github.com/flutter/flutter/issues/122966).
+
 ## 0.2.6
 
 * Reverts streaming frame support, as the implementation was incorrect and never

packages/camera/camera_windows/pubspec.yaml

@@ -2,7 +2,7 @@ name: camera_windows
 description: A Flutter plugin for getting information about and controlling the camera on Windows.
 repository: https://github.com/flutter/packages/tree/main/packages/camera/camera_windows
 issue_tracker: https://github.com/flutter/flutter/issues?q=is%3Aissue+is%3Aopen+label%3A%22p%3A+camera%22
-version: 0.2.6
+version: 0.2.6+1
 
 environment:
   sdk: ^3.3.0

packages/camera/camera_windows/windows/capture_controller.cpp

@@ -467,10 +467,15 @@ HRESULT CaptureControllerImpl::FindBaseMediaTypes() {
     return hr;
   }
 
+  return FindBaseMediaTypesForSource(source.Get());
+}
+
+HRESULT CaptureControllerImpl::FindBaseMediaTypesForSource(
+    IMFCaptureSource* source) {
   // Find base media type for previewing.
   if (!FindBestMediaType(
           (DWORD)MF_CAPTURE_ENGINE_PREFERRED_SOURCE_STREAM_FOR_VIDEO_PREVIEW,
-          source.Get(), base_preview_media_type_.GetAddressOf(),
+          source, base_preview_media_type_.GetAddressOf(),
           GetMaxPreviewHeight(), &preview_frame_width_,
           &preview_frame_height_)) {
     return E_FAIL;
@@ -479,8 +484,8 @@ HRESULT CaptureControllerImpl::FindBaseMediaTypes() {
   // Find base media type for record and photo capture.
   if (!FindBestMediaType(
           (DWORD)MF_CAPTURE_ENGINE_PREFERRED_SOURCE_STREAM_FOR_VIDEO_RECORD,
-          source.Get(), base_capture_media_type_.GetAddressOf(), 0xffffffff,
-          nullptr, nullptr)) {
+          source, base_capture_media_type_.GetAddressOf(), 0xffffffff, nullptr,
+          nullptr)) {
     return E_FAIL;
   }
 
@@ -566,15 +571,30 @@ void CaptureControllerImpl::StartPreview() {
 
   HRESULT hr = S_OK;
 
+  ComPtr<IMFCaptureSource> source;
+  hr = capture_engine_->GetSource(&source);
+  if (FAILED(hr)) {
+    return OnPreviewStarted(GetCameraResult(hr),
+                            "Failed to get capture engine source");
+  }
+
   if (!base_preview_media_type_) {
     // Enumerates mediatypes and finds media type for video capture.
-    hr = FindBaseMediaTypes();
+    hr = FindBaseMediaTypesForSource(source.Get());
     if (FAILED(hr)) {
       return OnPreviewStarted(GetCameraResult(hr),
                               "Failed to initialize video preview");
     }
   }
 
+  hr = source->SetCurrentDeviceMediaType(
+      (DWORD)MF_CAPTURE_ENGINE_PREFERRED_SOURCE_STREAM_FOR_VIDEO_PREVIEW,
+      base_preview_media_type_.Get());
+  if (FAILED(hr)) {
+    return OnPreviewStarted(GetCameraResult(hr),
+                            "Failed to set video preview output format");
+  }
+
   texture_handler_->UpdateTextureSize(preview_frame_width_,
                                       preview_frame_height_);
 

packages/camera/camera_windows/windows/capture_controller.h

@@ -181,6 +181,10 @@ class CaptureControllerImpl : public CaptureController,
   // for preview and video capture.
   HRESULT FindBaseMediaTypes();
 
+  // Enumerates video_sources media types and finds out best resolution
+  // for a given source.
+  HRESULT FindBaseMediaTypesForSource(IMFCaptureSource* source);
+
   // Stops preview. Called internally on camera reset and dispose.
   HRESULT StopPreview();
 

packages/camera/camera_windows/windows/test/capture_controller_test.cpp

@@ -153,6 +153,15 @@ void MockStartPreview(CaptureControllerImpl* capture_controller,
   MockAvailableMediaTypes(engine, capture_source.Get(), mock_preview_width,
                           mock_preview_height);
 
+  EXPECT_CALL(
+      *capture_source.Get(),
+      SetCurrentDeviceMediaType(
+          Eq((DWORD)
+                 MF_CAPTURE_ENGINE_PREFERRED_SOURCE_STREAM_FOR_VIDEO_PREVIEW),
+          _))
+      .Times(1)
+      .WillOnce(Return(S_OK));
+
   EXPECT_CALL(*engine, StartPreview()).Times(1).WillOnce(Return(S_OK));
 
   // Called by destructor