For example, the line FT_Index_Ignore_Attachment_Types=*.tif tells the indexer not to index attachments with the TIF extension. This can reduce the size of the index and hasten the return of search results. If you want to specify multiple file types to be ignored, separate them with a comma.
Examle:
FT_INDEX_IGNORE_ATTACHMENT_TYPES= *.png, *.rar, *.avi