converted videos in since deprecated formats to something still playable now?

If it is that, then I'd hope ffmpeg/avconv or VLC could do the job.

some of the old codecs are copyright-encumbered.

Where there's a will there's a way!

Thanks very much BP! I'll investigate all of those.

Vice versa, Smiffy & Ant: it converts a range of extant formats into MPX, a weird, deprecated proprietary format that will play on the redundant (but rather useful) player. 

What's the player do?

Ah, you're converting to an odd format.

It's a 1.5" player that fits snugly into a cavity in a wood-turning I've made.

Wot's wrong with microsd?

Probably something to do with microsd being a storage medium, not a video player.

In my poking around before, I saw mention that most MPX players also handled ...some other format...

...and in trying to recall what that other format was, I stumbled over this:
https://web.archive.org/web/20100815084506/http://www.kingston.com/support/PORTABLEMEDIAPLAYER/Transcoder.asp

"The PMP Transcoder is the KPEX100 tool that enables you to convert WMV, ASF, MPG, and AVI video files into the supported MPX format."

Had to download via Curl because Chrome sucks, but it did successfully convert an AVI - hopefully MPX is a single format, and doesn't do player-specific codec stuff or whatever...

I need to see a picture of this "player".

Ah. I clicked your link. The *screen* is 1.5". Unfortunately it appears the download link for the converter software doesn't work. Wow, the little fucker even came with *games*.

Cheers for all your chasing, BeeP, I'll give it a go. It's the most promising lead so far. It was definitely a shareware that various firms latched on to.

Particularly shit games, even for the time...

Sorry BP, I'm being thick. I've downloaded & unzipped Curl, but I can't find an executable file.

You don't have the MPX conversion app in a transferable form and size, do you?

https://www.dropbox.com/sh/p9t8qw2wuhb4hyj/AABj9q7HvbkIUCrHvdwyjgsga?dl=0

The setup exe is in the Transcode/English subfolder

What ^he^ said - I unzipped the PMPT.exe and ran Transcoder/English/setup.exe

I tried attaching just that setup folder (3.8MB zipped), but it didn't attach.

I assume the Dropbox link will work, but if not I can fling it over email.

Poor Manthorp. The malicious pixies of frustratingly-close-but-not-close-enough have made the program work perfectly but fixed the output resolution at 224x176 whereas his player will only accept 96x64. The program was designed to offer a range, but it looks like it's been messed with and the option is greyed out. 

Ta BP. I appreciate it