Alternative to MPEG Streamclip?

You could try HandBrake, or VLC.

I'd go with HandBrake first. If it can open those videos, it will be easy to transcode them.

VLC will almost certainly play them, but I have had more difficulty converting stuff.

Would EditReady work for you? https://www.divergentmedia.com/editready

El Capitan virtualized via VMware Fusion seems to run old 32-bit apps (MPEG Streamclip, Lightroom 6.14, Photoshop CS6 etc) in Catalina in light use OK. The documents can be on the Catalina's Desktop or some other shared folder and edited from the virtual machine. Mojave could also be virtualized but there are GUI artifacts (in Finder and Safari tabs etc) because there is no graphics acceleration (i.e. same as in Safe Boot).

I used MPEG Streamclip to convert all my iPad-incompatible old movies to H.264 mp4 over a year ago. MPEG Streamclip has not been updated in ages and it has some cosmetic visual artifacts in Mojave. The most severe artifacts can be fixed via Get Info > Open in low Resolution but even then it can't automatically resize the viewer and manual resizing is needed.

I still prefer MPEG Streamclip to losslessly trim large movies (from DJI Phantom 3 Pro etc) before archiving them. Yes, QuickTime Player can also quite nicely do that but it shows frames as decimals while MPEG Streamclip more accurately displays them as frames so fine-tuning the trim is easier. And MPEG Streamclip losslessly trims to the GOP while QuickTime Player re-encodes material outsides GOPs (material inside GOPs seems to be saved losslessly).

I recently tried several trimming utilities but didn't find anything as simple and elegant as MPEG Streamclip.

Free is good but sometimes paid is worth it. If you only need it once in a while free is good. I do quite a bit of transcoding and file type conversions to and from many different file types/codecs. For me Amerisoft Video Convertor is worth every penny for a lot of reasons. Check it out in the App Store.

Not quite sure what you are doing but would HandBrake do the job?

https://handbrake.fr

Also you may be able to use the Finder.

Right click a video fie and see if you have the option.

Recent OS versions can do this:

Pretty sure High Sierra will do the trick.

Catalina will for sure and newer OS versions.

I would keep that older 32 bit compatible Mac handy. 😀​👍​

Al

Another one to perhaps consider is ff-Works. It's paid though.

That's a neat trick!

Using the Finder is great but won’t work in Catalina if the problem are old 32-bit codecs.

But sure if one has Access to a mac with an older OS.