ffmpeg tweaks (#121)

* save reports from ffmpeg concat process

* let ffmpeg determine thread count by default

* disable stdin for ffmpeg processes

ErsatzTV.Infrastructure/Migrations/20210331010449_Update_FFmpegProfile_ThreadCount.cs

@@ -0,0 +1,14 @@
+using Microsoft.EntityFrameworkCore.Migrations;
+
+namespace ErsatzTV.Infrastructure.Migrations
+{
+    public partial class Update_FFmpegProfile_ThreadCount : Migration
+    {
+        protected override void Up(MigrationBuilder migrationBuilder) =>
+            migrationBuilder.Sql(@"UPDATE FFmpegProfile SET ThreadCount = 0 WHERE ThreadCount = 4");
+
+        protected override void Down(MigrationBuilder migrationBuilder)
+        {
+        }
+    }
+}