TASK 4 ship step 3: encoder + RTMP push — FFmpeg subprocess with probed H.264 picker, BGRA stdin feed, stderr health parsing, graceful stop — 122 tests passing, 0 warnings

Services/Encoder/FfmpegEncoderPicker.cs

@@ -0,0 +1,35 @@
+namespace ytLive.Services.Encoder;
+
+/// <summary>
+/// Picks the best available H.264 encoder from ffmpeg's <c>-encoders</c> listing,
+/// honoring the license posture (no GPL libx264): hardware NVENC → QSV → AMF, then
+/// the OpenH264 software fallback. Pure parser — the <c>-encoders</c> probe output is
+/// fetched by the encoder via an <see cref="IEncoderProcess"/> and fed here.
+/// </summary>
+public static class FfmpegEncoderPicker
+{
+    /// <summary>Preference order, best first. All ship in the pinned BtbN lgpl-shared build.</summary>
+    public static readonly string[] Preference =
+    [
+        "h264_nvenc",
+        "h264_qsv",
+        "h264_amf",
+        "libopenh264",
+    ];
+
+    /// <summary>
+    /// First <see cref="Preference"/> entry present in the probe output, or the
+    /// software fallback (which the pinned build always contains) if none matched.
+    /// Never returns libx264 — it is GPL and would contaminate the paid product.
+    /// </summary>
+    public static string Pick(string probeOutput)
+    {
+        var available = probeOutput.Split('\n');
+        foreach (var name in Preference)
+        {
+            if (available.Any(line => line.Contains(name, StringComparison.Ordinal)))
+                return name;
+        }
+        return Preference[^1];
+    }
+}