Add configurable FFmpeg log level

- Add FfmpegLogLevel property to EncodingOptions (default: 'error')
- Use configuration value in GetInputModifier instead of hardcoded value
- Allows changing log verbosity without rebuild via encoding.xml
- Possible values: quiet, panic, fatal, error, warning, info, verbose, debug, trace

MediaBrowser.Model/Configuration/EncodingOptions.cs

@@ -59,6 +59,7 @@ public class EncodingOptions
         EnableSubtitleExtraction = true;
         AllowOnDemandMetadataBasedKeyframeExtractionForExtensions = ["mkv"];
         HardwareDecodingCodecs = ["h264", "vc1"];
+        FfmpegLogLevel = "error";
     }
 
     /// <summary>
@@ -295,4 +296,9 @@ public class EncodingOptions
     /// Gets or sets the file extensions on-demand metadata based keyframe extraction is enabled for.
     /// </summary>
     public string[] AllowOnDemandMetadataBasedKeyframeExtractionForExtensions { get; set; }
+
+    /// <summary>
+    /// Gets or sets the FFmpeg log level (quiet, panic, fatal, error, warning, info, verbose, debug, trace).
+    /// </summary>
+    public string FfmpegLogLevel { get; set; }
 }