This is four years after user13832229 answer, and I ran into the same issues. Error was pydub\utils.py:198: RuntimeWarning: Couldn't find ffprobe or avprobe - defaulting to ffprobe, but may not work on Win11 machine.

As way of background, worked fine on dev machine in venv at 3.10.5, but I want to compile by pyinstaller, and be able to ship an executable to other people. I compressed ffmpeg and ffprobe into the exe, so the end user did not need to worry about installing these packages. Although the package would nicely uncompress in a temp directory, where I could use them using CLI, pydub would not recognize them no matter what environmental variable I tried to lock down. Also, didn't matter if it was in PATH environmental variable. Just would not work. (And even if it did work, I wasn't keen on depending on setting this to make a program work.)

So, stumbled across this comment of simply copying ffprobe and ffmpeg to same directory as mp3 file, and this is the only thing that worked.

I'm hoping to set a note on the internet so others can see that this seems to be the best practical way of solving what is strange issue.