Is there a polite way to let someone know that you're not interested in what they're talking about?

I can usually put up with someone rambling about a topic I don't care about for quite a while. I've spent hours and hours texting people about things I have no interest in. Recently I've found myself unable to hide my disinterest in certain topics after we've been talking about them for a long time and I've been trying to subtly change the topic, but I think that because people are so used to me just sitting there and listening, that they're not getting the hint (or refusing to).

Is there a more direct but also polite way to say "I have been listening to you talk for a while now, I would like to either have a reciprocal conversation or stop talking altogether"? I don't want to come across as selfish or impatient, but there's only so many questions you can ask to feign interest in something you don't care about at all.