perf(video): move tier scaling to ffmpeg

The frame pump now submits crop-sized BGRA frames; FFmpeg scales them to final tier dimensions. Bundled scaler benchmark: 300 608x1080 to 1080x1920 frames in 0.435s (scaler-only).

Reference: https://ffmpeg.org/ffmpeg-filters.html#scale-1

Services/Encoder/FfmpegArgs.cs

@@ -19,7 +19,7 @@ public static class FfmpegArgs
             "-hide_banner", "-loglevel", "info",
             "-stats", "-stats_period", "0.5",
             "-f", "rawvideo", "-pix_fmt", "bgra",
-            "-video_size", $"{options.Width}x{options.Height}",
+            "-video_size", $"{options.RawWidth}x{options.RawHeight}",
             "-framerate", options.Fps.ToString(),
             "-i", "pipe:0",
             "-f", "f32le", "-ar", options.AudioSampleRate.ToString(),
@@ -53,6 +53,10 @@ public static class FfmpegArgs
     {
         var gop = options.GopSize;
         args.AddRange(["-map", "0:v", "-map", "1:a"]);
+        if (options.RawWidth != options.Width || options.RawHeight != options.Height)
+        {
+            args.AddRange(["-vf", $"scale={options.Width}:{options.Height}:flags=bilinear,setsar=1"]);
+        }
         args.AddRange(["-c:v", videoEncoder]);
         args.AddRange(["-b:v", $"{options.BitrateKbps}k", "-maxrate", $"{options.BitrateKbps}k",
             "-bufsize", $"{options.BitrateKbps * 2}k"]);