Fix potential garbled text in FFmpeg logs on Windows

Explicitly set StandardErrorEncoding and StandardOutputEncoding to
Encoding.UTF8 when invoking the FFmpeg subprocess.

This prevents log encoding issues and character corruption on Windows
environments that default to non-UTF8 ANSI code pages.

This fixes garbled metadata and font names in the FFmpeg logs.

Signed-off-by: nyanmisaka <nst799610810@gmail.com>

MediaBrowser.MediaEncoding/Encoder/EncoderValidator.cs

@@ -6,6 +6,7 @@ using System.Diagnostics;
 using System.Globalization;
 using System.Linq;
 using System.Runtime.Versioning;
+using System.Text;
 using System.Text.RegularExpressions;
 using MediaBrowser.Controller.MediaEncoding;
 using Microsoft.Extensions.Logging;
@@ -645,7 +646,9 @@ namespace MediaBrowser.MediaEncoding.Encoder
                     WindowStyle = ProcessWindowStyle.Hidden,
                     ErrorDialog = false,
                     RedirectStandardInput = redirectStandardIn,
+                    StandardOutputEncoding = Encoding.UTF8,
                     RedirectStandardOutput = true,
+                    StandardErrorEncoding = Encoding.UTF8,
                     RedirectStandardError = true
                 }
             })