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/IEncoderProcess.cs

@@ -0,0 +1,26 @@
+using System.Diagnostics;
+using System.IO;
+
+namespace ytLive.Services.Encoder;
+
+/// <summary>
+/// Seam around a spawned subprocess (the encoder's ffmpeg and the encoder probe).
+/// Exposes the redirected stdin (binary frames), stdout (probe listing) and stderr
+/// (progress lines) plus exit control, so the encoder logic never touches
+/// <c>System.Diagnostics.Process</c> directly and tests can fake the whole thing.
+/// </summary>
+public interface IEncoderProcess : IDisposable
+{
+    void Start(ProcessStartInfo startInfo);
+
+    /// <summary>Raw binary stdin — the encoder writes BGRA frames here.</summary>
+    Stream StandardInput { get; }
+
+    TextReader StandardOutput { get; }
+    TextReader StandardError { get; }
+
+    bool HasExited { get; }
+    int ExitCode { get; }
+    void Kill();
+    Task WaitForExitAsync(CancellationToken cancellationToken = default);
+}