I've used ffmpeg to make a series of videos from pictures of size 600x373.

I'm now trying to bring those into kdenlive but I've noticed that my default setting (dv pal) leaves black borders on either side of it. I've tried resizing the frame in the profiles section but then that just warps the image more.

I've done a bit of research on pixel aspect ratios and even found something that will help calculate it (http://www.digitalrebellion.com/pixel_calc.htm) but I'm still really lost and confused. I tried setting the pixel aspect ratio to 1:1 in a new profile but still getting warped images.

How could I render the movie to exactly 600x373? What settings do I need to use?

You should only change the pixel aspect ratio if it looks stretched in either direction. If you want to get rid of black bars on either side use the Crop effect. The latest version of Kdenlive includes a Center checkbox to automatically scale and crop to fill the project screen.

Thanks a lot!