Can't find codec, camera refused connection

[IntellectualFool]

I struggled for a couple of days working through an issue after moving my vbox virtual machine to a new host and upgrading the guest running zoneminder, so I thought I would join this forum and share my experience and the solution.

My virtual machine had been running on a Mac Mini when that machine gave out (don't get me started on my frustration with Apple...). I migrated the VM to a Linux machine running openSUSE 15.5 Leap, and I updated the guest VM (also running 15.5. Leap), when zoneminder stopped working. I was caught up in working through other details of the migration (external storage, ...), and I lost site of zoneminder migration until after getting storage issues worked out.

Zoneminder refused to start capturing my Amcrest 2M-841B rtsp camera streams with the following messages (paraphrased):
Can't find codec for video stream from rtsp:...
and later
Unable to open input rtsp:... due to: Server returned 404 Not Found
refused to connect

I enabled debug logging, and located a message indicating H264_MMAL could not be found, but research on this forum indicated that error was just a developer comment, not a real problem, but the forum posting indicated they worked through their issue by changing the installed ffmpeg version, so I tried that and it fixed the problem on my machine.

After the VM update, I was running ffmpeg-6 and it refused to work with the rtsp stream from my Amcrest camera under zoneminder. ffplay usually worked but it was somewhat unreliable, sometimes reporting that the camera refused to connect. I downgraded to ffmpeg-4 (ffmpeg-5 was not listed in my package manager) and the problem disappeared, video capturing restored and ffplay also reliably connected to the camera.