ytLlive/Services/Compositor/StaticPixelCache.cs

using System.IO;
using System.Windows.Media;
using System.Windows.Media.Imaging;

namespace ytLive.Services.Compositor;

/// <summary>
/// Decodes a layout asset's bytes into a tightly-packed BGRA8 <see cref="VideoFrame"/>
/// once per content-hash asset id. The preview uses the WPF <c>BitmapImage</c> in
/// ImageCache; the output path needs raw pixels, so assets decode here instead.
/// </summary>
public static class StaticPixelCache
{
    private static readonly Dictionary<string, VideoFrame> Cache = new(StringComparer.Ordinal);

    public static VideoFrame? Get(string assetId)
    {
        if (string.IsNullOrWhiteSpace(assetId)) return null;
        if (Cache.TryGetValue(assetId, out var frame)) return frame;

        var bytes = LayoutStore.Instance?.GetAssetBytes(assetId);
        if (bytes == null || bytes.Length == 0) return null;

        var decoded = Decode(bytes);
        if (decoded != null) Cache[assetId] = decoded;
        return decoded;
    }

    public static VideoFrame? Decode(byte[] bytes)
    {
        try
        {
            using var stream = new MemoryStream(bytes, writable: false);
            var decoder = BitmapDecoder.Create(stream, BitmapCreateOptions.PreservePixelFormat, BitmapCacheOption.OnLoad);
            var source = decoder.Frames[0];
            var bgra = new FormatConvertedBitmap(source, PixelFormats.Bgra32, null, 0);
            var width = bgra.PixelWidth;
            var height = bgra.PixelHeight;
            var pixels = new byte[width * height * 4];
            bgra.CopyPixels(pixels, width * 4, 0);
            return new VideoFrame(width, height, pixels);
        }
        catch
        {
            return null;
        }
    }
}