Slideshow shared as DVD is strenched

Hi , I’m just working on a wedding slideshow which I have shared as a DVD . Problem is the completed DVD when played is stretched , with the vertical images showing as square pictures .
This shared as a mpv file and was burnt using toast .
How do I export the slideshow to be played as edited to a DVD ?

thanks in advance.

when you open the exported file in QuickTime player before burning it using toast, is it also stretched?

The exported m4v file is stretched, but the quicktime file has the correct dimensions … I have burnt the quicktime files to DVD for the client , but I do want this issue resolved … any ideas ?