ytLlive/Services/MediaCaptureFrameSource.cs

using System;
using System.Linq;
using System.Runtime.InteropServices;
using System.Runtime.InteropServices.WindowsRuntime;
using System.Threading.Tasks;
using Windows.Graphics.Imaging;
using Windows.Media.Capture;
using Windows.Media.Capture.Frames;
using Windows.Media.MediaProperties;
using ytLive.Helpers;

namespace ytLive.Services;

/// <summary>
/// CPU-first MediaCapture source. Requests BGRA8 frames from the camera's video
/// preview source; the capture pipeline does any format conversion, so every
/// frame arrives as a normalized <see cref="VideoFrame"/>. Frames arrive on a
/// worker thread — marshal before touching WPF.
/// </summary>
public sealed class MediaCaptureFrameSource : ICameraFrameSource
{
    private readonly string _deviceId;
    private MediaCapture? _capture;
    private MediaFrameReader? _frameReader;

    public string DeviceId => _deviceId;

    public event Action<VideoFrame>? FrameAvailable;

    public MediaCaptureFrameSource(string deviceId)
    {
        _deviceId = deviceId;
    }

    public async Task StartAsync()
    {
        var capture = new MediaCapture();
        MediaFrameReader? reader = null;
        try
        {
            var settings = new MediaCaptureInitializationSettings
            {
                VideoDeviceId = _deviceId,
                StreamingCaptureMode = StreamingCaptureMode.Video,
                MemoryPreference = MediaCaptureMemoryPreference.Cpu,
                SharingMode = MediaCaptureSharingMode.SharedReadOnly,
            };
            await capture.InitializeAsync(settings);

            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)
            {
                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;
            await reader.StartAsync();

            _capture = capture;
            _frameReader = reader;
        }
        catch
        {
            if (reader != null)
            {
                reader.FrameArrived -= OnFrameArrived;
                reader.Dispose();
            }
            capture.Dispose();
            throw;
        }
    }

    public async Task StopAsync()
    {
        var reader = _frameReader;
        _frameReader = null;
        if (reader != null)
        {
            reader.FrameArrived -= OnFrameArrived;
            try
            {
                await reader.StopAsync();
            }
            catch (Exception ex)
            {
                AppLog.Write($"MediaCaptureFrameSource: stop frame reader failed: {ex.Message}");
            }
            reader.Dispose();
        }

        var capture = _capture;
        _capture = null;
        capture?.Dispose();
    }

    private void OnFrameArrived(MediaFrameReader sender, MediaFrameArrivedEventArgs args)
    {
        using var frame = sender.TryAcquireLatestFrame();
        var videoFrame = frame?.VideoMediaFrame?.SoftwareBitmap;
        if (videoFrame == null) return;

        var bitmap = videoFrame.BitmapPixelFormat == BitmapPixelFormat.Bgra8
            ? videoFrame
            : SoftwareBitmap.Convert(videoFrame, BitmapPixelFormat.Bgra8);

        try
        {
            using var buffer = bitmap.LockBuffer(BitmapBufferAccessMode.Read);
            using var reference = buffer.CreateReference();
            if (WindowsRuntimeMarshal.TryGetDataUnsafe(reference, out var pixelsPtr, out var capacity))
            {
                var pixels = new byte[capacity];
                Marshal.Copy(pixelsPtr, pixels, 0, (int)capacity);
                FrameAvailable?.Invoke(new VideoFrame(bitmap.PixelWidth, bitmap.PixelHeight, pixels));
            }
        }
        catch (Exception ex)
        {
            AppLog.Write($"MediaCaptureFrameSource: frame copy failed: {ex.Message}");
        }
        finally
        {
            if (!ReferenceEquals(bitmap, videoFrame))
                bitmap.Dispose();
        }
    }
}