update thumbnail sampling

MediaBrowser.MediaEncoding/Encoder/MediaEncoder.cs

@@ -915,7 +915,7 @@ namespace MediaBrowser.MediaEncoding.Encoder
             var mapArg = imageStreamIndex.HasValue ? (" -map 0:v:" + imageStreamIndex.Value.ToString(CultureInfo.InvariantCulture)) : string.Empty;
 
             var enableThumbnail = !new List<string> { "wtv" }.Contains(container ?? string.Empty, StringComparer.OrdinalIgnoreCase);
-            var thumbnail = enableThumbnail ? ",thumbnail=30" : string.Empty;
+            var thumbnail = enableThumbnail ? ",thumbnail=24" : string.Empty;
 
             // Use ffmpeg to sample 100 (we can drop this if required using thumbnail=50 for 50 frames) frames and pick the best thumbnail. Have a fall back just in case.
             var args = useIFrame ? string.Format("-i {0}{3} -threads 0 -v quiet -vframes 1 -vf \"{2}{4}\" -f image2 \"{1}\"", inputPath, tempExtractPath, vf, mapArg, thumbnail) :