I have a video clip (.mpg) that was extracted from an old Hitachi camera with a damaged disc. When I play it either in kdenlive or the original video acquisition software, it has tiny glitches, barely noticeable. They would be fine. However, if I render it or play it in just about anything else, the video freezes twice for half a minute each time (audio plays through and when the video resumes it is synchronized). That includes if I upload it to YouTube, which I will want to do.

Like, if I render it into a png image sequence, the images do not match the moving images displayed on the clip monitor - it yields the same image hundreds of times in a row.

Is there some way to tell it to recode whatever video it was showing on the monitor, bypassing whatever screwup it's making when rendering?
Suspecting that it was only the fact that it was just copying the file over in unchanged regions, I wanted to try making a noise segment, overlaying it on the normal video, and setting it to be 99.5% transparent, but the alpha operations didn't seem to actually enable transparency - is there a way to do that?

Now… I'm using kdenlive 0.9.10 as that's the latest from MacPorts. That's old. If this has been fixed on linux, maybe I can scrounge up a linux box to do it in. Or if it's reasonably possible to build something more recent on a mac, I can try that. Also, my ffmpeg is version 3.4.2.

I can post the video - it's 155 Mb. What's a good host?

Solved my problem by using a different program that appears based on strong interface similarities to be based on a more recent version of kdenlive - OpenShot Video Editor.

I ran into a few other oddities, but I imagine they've been fixed by now.

working with a damaged clip is not a good way ... you have FIRST to try to fix the damaged video.. you can use a lot of video fixer (Usually for Windows) ... also VLC have an integrated tool to fix bad/incomplete videos, also you can try to convert the Video to another format...
when you have "readable" file.. you can save it.. and use your preferred video editing tool ( personally.. i don't like OpenShot )