DVD doesn’t have HD.
DVD uses MPEG2 as video codec, which is way less efficient than AVC or even HEVC.
I propose this MO:
- rip the DVDs without changing the codec or resolution, using Makemkv (Google it)
- append the parts to get a complete movie, following this HowTo [HowTo]: joining multi-part movies files with MKVtoolnix GUI
- Employ Handbrake to convert the MPEG2 codec to AVC, to remove the black borders and to remove the interlacing if necessary.