Hello dogisay,
Thank you for your post.
At the present time you can add the Media list of Video Splitter 6 the files with the same: format, video and audio codec, resolution, bitrate and frame rate. If files have some differences, then you'll see such "Some files were ignored because of unmatched content with existing in the list" information notice.
So, please select files of the same characteristics (format, video, audio content) to add them to Media list of Video Splitter 6.