Something like this might work if you plug it in to your cable box audio outputs. The audio level out of the RCA jacks may not be enough to drive your headphones though. You can probably find the adapter at a local electronics store.
If you're lucky, you might already have an audio device that might have RCA audio inputs and a headphone jack. Some iPod docks or portable stereos have these.
Other options are to purchase a headphone amplifier or wireless headphones.
I need to use headphones on my T.V. at night because of complaining roommates but found there's no audio out headphone jack. I have empty RCA audio out connectors but am not sure if an adapter would do what I want. I need the T.V. speakers to go quiet and I have a digital cable box connected to AV1 so will the headphones recognize that? Any help is appreciated, thanks