VOB editing with FFMPEG
In the first step you are doing a lossy conversion, you transcode from vob to mp4, and then to ts. For a lossless re-mux you should just re-mux, better to specify both video and audio:

ffmpeg -i VTS_01_1.VOB -c:v copy -c:a copy -bsf:v h264_mp4toannexb -f mpegts intermediate1.ts


However, if you re-mux for the purpose of slicing then you should be aware that with this method it is possible only on exact keyframe boundary, so you might want to reconsider whether you want to do it this way. For a detailed explanation please see in this answer.