The source material for a DVDSCR is, by definition, standard definition (480p or 576p). It is often mastered on a DVD, which utilizes the MPEG-2 codec—a codec that is efficient enough for playback but requires higher bitrates to avoid artifacts. However, when modern compression standards (like x264 or x265) are applied to these sources, they can usually compress the file significantly without visible quality loss.
Downloading or distributing a DVDSCR release is a violation of copyright law. These versions are strictly for promotional use, and their unauthorized release often leads to legal action against the original "leaker" who was entrusted with the disc. If you'd like to learn more, let me know: bloat dvdscr