The replays are, best I can tell, a set of inputs or orders for the game rather than an actual recording. If you want to upload them, the simplest way is likely to get a screen recorder - like OBS - and record the replays that way.
That'd explain why replays break between versions and also would make the "edit replay" feature easier to implement so it's a quite clever way to save them.
Most modern fighting games actually handle replays this way, because its significantly cheaper on storage and still deterministic(often they'll have a ver-number appended so that differences can be reverted for playback)
