With the release of mpegtools by Marcus Lundblad, it is now possible to create an MPEG file from within BeOS, including video material edited in personalStudio.
„mpegtools“ is able to work with the Pegasus codec optionally used by personalStudio on analog export, so this should be the output codec used. For best results, I have used the following process:
Save output from personalStudio:
Format: Quicktime
Size: 360×240 (if original source is DV – else, or nearest size)
Codec: Pegasus
FPS: whatever (I use 29.97 with NTSC DV input)
Quality Factor = 99
(Note: this is important – we need to ensure max. quality for this intermediate stage, so selecting 100 would seem to be the natural choice. However, 100 seems to equate to no compression, and the mpeg encoder does not understand the resulting video info. Hence, quality = 99).
Convert Quicktime file to MPEG-I:
Execute binary found in the mpegtools/bin directory, i.e.:

mpeg2enc infile.mov -q 5 -o outfile.mpg

(the q 5 [= quality 5] setting seems to give the best appearance/playback performance compromise)
mpegtools also allows the encoding of MPEG-II video files, so there’s no reason that we can’t output a 640 (or 720) width QuickTime file from personalStudio and convert to MPEG-II.