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Webcam grab: SharedReadOnly mode, VideoPreview/VideoRecord source fallback, name the blocking app in the error (NVIDIA Broadcast finding)

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This commit is contained in:
Llama Chile Shop
2026-08-06 14:42:54 -07:00
parent 98cdc4b3f4
commit b64830ed11
2 changed files with 23 additions and 7 deletions
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Services/MediaCaptureFrameSource.cs
+11 -4
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@@ -43,14 +43,21 @@ public sealed class MediaCaptureFrameSource : ICameraFrameSource
VideoDeviceId = _deviceId,
StreamingCaptureMode = StreamingCaptureMode.Video,
MemoryPreference = MediaCaptureMemoryPreference.Cpu,
SharingMode = MediaCaptureSharingMode.SharedReadOnly,
};
await capture.InitializeAsync(settings);
var colorSource = capture.FrameSources
.FirstOrDefault(pair => pair.Value.Info.MediaStreamType == MediaStreamType.VideoPreview)
.Value;
var colorSource = capture.FrameSources.Values
.OrderBy(s => s.Info.MediaStreamType == MediaStreamType.VideoPreview ? 0 : 1)
.FirstOrDefault(s => s.Info.MediaStreamType is MediaStreamType.VideoPreview or MediaStreamType.VideoRecord);
if (colorSource == null)
throw new InvalidOperationException($"No video preview source on camera '{_deviceId}'.");
{
var kinds = string.Join(", ", capture.FrameSources.Values
.Select(s => s.Info.MediaStreamType).Distinct());
throw new InvalidOperationException(
$"Camera '{_deviceId}' exposes no video source (found: {kinds}). " +
"It may be locked by another app (e.g. NVIDIA Broadcast).");
}
reader = await capture.CreateFrameReaderAsync(colorSource, MediaEncodingSubtypes.Bgra8);
reader.FrameArrived += OnFrameArrived;
ai.md
+12 -3
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@@ -84,10 +84,19 @@ C# / WPF (.NET 8) following MVVM:
- **Seam-first:** everything above the WinRT layer speaks only `VideoFrame` (normalized tightly-packed
BGRA8) + `CameraDeviceInfo`/`ICameraEnumerator`/`ICameraFrameSource` interfaces. Tests inject fakes;
screen capture and background removal later feed the same seam.
- **CPU-first:** `MediaCaptureInitializationSettings { MemoryPreference = Cpu, StreamingCaptureMode = Video }`,
frames pulled via `CreateFrameReaderAsync(colorSource, MediaEncodingSubtypes.Bgra8)` — the pipeline does
any format conversion, so every `FrameArrived` yields a ready BGRA8 `SoftwareBitmap` (bytes read via
- **CPU-first:** `MediaCaptureInitializationSettings { MemoryPreference = Cpu, StreamingCaptureMode = Video,
SharingMode = SharedReadOnly }`, frames pulled via
`CreateFrameReaderAsync(colorSource, MediaEncodingSubtypes.Bgra8)` — the pipeline does any format
conversion, so every `FrameArrived` yields a ready BGRA8 `SoftwareBitmap` (bytes read via
`WindowsRuntimeMarshal.TryGetDataUnsafe`, not marshalled copies).
- **Source pick, not first hit:** the frame reader is bound to the first source that is `VideoPreview`
(preferred) or `VideoRecord`, not blindly the first preview source. If a camera exposes neither, the
failure names the device and the stream types it *does* expose. `SharedReadOnly` lets the capture
coexist with other apps that share the camera.
- **Known failure: NVIDIA Broadcast** — it opens the physical webcam exclusively, so `InitializeAsync`
fails with "camera in use" (or, if init slips through, the device exposes no preview source). Fix:
quit Broadcast while streaming, or pick its virtual "NVIDIA Broadcast" device from the picker and the
app captures the processed feed. This is a real-device finding (Logitech `VID_046D&PID_082D`).
- **TFM:** `net8.0-windows10.0.19041.0` (app + tests) pulls the WinRT projection from the SDK reference
packs — no NuGet package, no capability manifest (unpackaged desktop app works; the Windows privacy
camera toggle still applies). `EnableWindowsTargeting` keeps WSL builds working.