They came in as .ogg?? I thought you converted to dvd? Are you talking about then ripping the DVD video with HandBrake or something?
Also, you're doing something wrong, or at least have your file extension -> "open with" settings screwed up if renaming a .ogg to a .mp4 is necessary. Maybe it opens with a different player then, and only the player associated with .mp4 is actually working on your computer? (.ogm is the usual extension for ogg video; Maybe you have .ogg associated with an audio-only player?)
Anyway, you're doing several steps here:
- capture a digital version of the video signal from your VCR
- encode that to MPEG2 dvd
- transcode the lossy MPEG2 to something a video codec that can go in a .ogg container.
The achievable quality of step 1 is fairly limited, since the representation stored on the magnetic VHS tapes is of limited quality.
Because of the limited quality of the source, you're probably not losing much quality from having a lossy intermediate codec. Obviously it would be better to go directly from capture -> final, with only lossless steps in between (e.g. capture card in a computer, capture to a lossless file. Or encode in realtime to the final format.)
You ARE probably losing quality if your final output is going into an ogg container, though. It's probably Theora video, which is obsolete (and has a much worse quality vs. bitrate tradeoff than VP8 or x264).
A player like VLC or mpv will let you see the codec details of your video. Or just use mediainfo.
Unless you're archiving in a lossless format (50x the filesize of visually-indistinguishable lossy), you might want to apply some filtering to clean up the video from the VHS tapes before encoding. Depending on the condition of the tapes, they might have significant chroma noise that a denoise filter could help with. This will require some playing around.
You'll want to read up on video codecs to make a decision on which one to use for archival storage. VP8 and VP9 are free from patent royalties. h.264 and h.265 aren't, but patents don't live forever, and h.264 is the current playable-by-everything standard for video. You'll want to check up on the patent royalty situation, but as long as you aren't selling access to h.264 video, you shouldn't owe any fees. The best h.264 encoder in the world is x264, which is free and open source, and very mature and well optimized.
h.265 is next-gen, and x265 is still very slow, but can get better quality at the same bitrates as x264. Google's VP9 encoder is somewhat better than x264 for quality-per-bitrate, but takes at least 10x longer to encode. VP8 is not bad, but I think it's a bit worse quality-per-bitrate (aka rate-distortion) compared to x264. (both with near-maxed CPU-usage settings).
If you want library patrons to play files on their own devices right now, I'd suggest going with h.264 because of the massive compatibility advantage over any other format. If we're only talking about playback on library-owned computers, I might play around with VP9.
For future-proofing, every player for the next 50 years at least will support h.264, I'd guess. I think H.264 for video will be like mp3 for audio: people will still be using it LONG after it's obsolete, because it's the first format that doesn't completely suck, and that has widespread player support for everything from streaming to files to videoconferencing.