Don't pass through timestamp for image extractor (#13999)

MediaBrowser.MediaEncoding/Encoder/MediaEncoder.cs

@@ -756,7 +756,7 @@ namespace MediaBrowser.MediaEncoding.Encoder
                 _threads,
                 vf,
                 isAudio ? string.Empty : GetImageResolutionParameter(),
-                EncodingHelper.GetVideoSyncOption("0", EncoderVersion).Trim(), // passthrough timestamp
+                EncodingHelper.GetVideoSyncOption("-1", EncoderVersion).Trim(), // auto decide fps mode
                 tempExtractPath);
 
             if (offset.HasValue)