How to set a space in the file name?

Question

cmd/bat

for %%i in (*.mp4) do (
  for %%a in (*.wav) do (
    echo %%i
    echo %%a
    ffmpeg -i %%i -i %%a -c:v copy -map 0:v:0 -map 1:a:0 -shortest %%~ni_.mp4
  )
)

I was looking for a way to set the parameters in such a way that, in case of frequent use, I would not enter names for files, but only their extensions. Found only one option. But I don't understand how to set the name in quotes so that files with spaces are not ignored.