I got the message, and decided to go get avconv, which is not in the repo. So I downloaded the file avconv.zip from sourceforge,
and extracted it, but it looks like a Windows program. Here's what the extraction produced:
inflating: setup.exe <-----
inflating: AVConv_1_0_0_1/AVConv.exe.deploy <----
inflating: AVConv_1_0_0_1/AVConv.exe.manifest <----
So now what? I see above "if you do not use this program it is possible to uninstall it."
I don't like to dump any kind of media player--sooner or later, something will come along that needs it to play.
I do have ffmpeg, but not all the java stuff that seems to go with it, but synaptic said I would need avconv or As Converter,
which I haven't looked for, except it's not in the repo either.