can you get access to a Linux shell? A Bash Shell? Probably you can.
you need to get a group of tools called 'ffmpeg' and load them so you can access them through a shell.
then you can do the converions and encoding, and even make mp4s out gifs and audio files.
but to do a png to jpg it is as simple as
convert somefilename.png someothername.jpg
I do that as well to make sure that no exiv data is left in a file too.
there are all kinds of command line options to use in that too, you can change the resolutions and sizes of the files as well.