Audio problem with videos transferred to tablet

Hello folks. I’ve recently purchased an iPad patch cord from Apple that will allow me to play movies that I’ve purchased from iTunes over a projector, with a set of standard desktop speakers plugged into the headphone jack.

It all works fine with these iTunes-purchased movies. I get the picture on the projection screen and the sound from the disktop speakers.

However, if I try the same thing with a movie that I have converted from one of my DVDs, the sound is cut off from the headphone jack.

Since I cannot purchase all the movies I want on my iPad through iTunes (at least not so far), I really want to be able to convert some of my DVDs for this purpose.

My question is: could there be some audio track(s) that are not surviving the conversion process so that the headphone jack does not receive the signal with these files (whereas it does receive a signal from the iTunes movies)? And, if so, is there some adjustment I need to make when converting the films so that this audio track is still in the file when it moves over to my iPad?

The part that really confuses me is the fact that, when I unplug the patch cord, the sound does play through the speakers with these files (but of course, in that case, the video is only playing on the tablet screen, not the projector). I have experimented with only plugging the yellow video plug into the projector and leaving the white and red audio plugs hanging loose, but this doesn’t have any effect. If the patch cord is plugged into the iPad, the sound doesn’t play through the speakers on these converted files.)

I really hope you can help me out here. Thanks in advance!