I have found a small number of swf videos on an old backup drive that I have but I have found that I can't play them anymore. Is there any system out there that actually works where I can convert these files to mp4 - I have tried realplayer but nothing seems to happen.
Yes there seem to be a good number of programs with that feature. Not real sure which works. First I will say beware of a drop in visual quality. All to common with conversions.
Someone seems to have answered how to do that with Adobe After Effects here. https://community.adobe.com/t5/animate/converting-swf-files-into-mov-or-mp4-files-using-after-effect...
If you wish to play your files without changing the format you can download a Standalone Flash / SWF player to play them offline. The one from adobe itself can be found here https://www.adobe.com/support/flashplayer/debug_downloads.html Download and install Flash Player projector. Then play your swfs with it. Most swfs will play more or less as originally intended in it.
Alternatively if you have an internet site of your own that you are displaying these swfs on I suggest using ruffle.rs to playback your swf files. It should play them like normal but as webassembly. The code is a work in progress and I hear they are happy to help.
If you would like to archive your swfs first I suggest doing so with https://bluemaxima.org/flashpoint/ or the Internet Archive.
If it's an actual SWF with a video embedded in it, playing it back with the standalone player is probably the easiest path. A quick google for "extract video from SWF" turned up a number of third-party tools, but I can't vouch for any of them.
If it was an actual Flash video file (FLV), then dropping it into a converter like Adobe Media Encoder would be a straightforward proposition.
Downloaded Adobe Flash Flayer 32 and tried to open various swf files, but get the same message every time "This content doesn't seem to be working. Try again later". I also downloaded a standalone player (SWF File Player) but could not play videos on this either. I seem to be doing something wrong but not sure what. Any other advice?