I note that on other posts a Y adapter with two of the RCA/Phono plugs and a headphone socket is suggested. If your TV has the Red and White Audio OUT RCA sockets as well as the more common Red and White Audio IN sockets that is a good idea, and the Audio signal from these sockets will not be affected by the TV speaker volume, which can be turned off.
Another neat solution is described below.
If you have a european TV with a SCART 20 pin connector there is an easy way to make an adapter to use with headphones which have a small stereo jack. (1/4 inch jacks are too big to fit inside the SCART plug, but the wiring advice still applies).
Buy a male SCART plug and also a mini jack socket (both easily found on the internet. Even better if you have one is to take a pre-wired headphone extension lead and cut the moulded-on socket off, leaving a few inches of cable attached to it . When you strip back to bare wires, there will be a a very thin and delicate Red wire, a Green wire, and a bare copper braid. Solder the wires as follows Red wire to PIN 1 of the SCART, Green wire to Pin 3 of the SCART and the copper braid to Pin 4 of the SCART. When looking at the solder terminals of the SCART turn it so that the straight end is to your right and the angled end to the left. Pin 1 is the first pin on the right on the bottom row (Audio Out Right channel) Pin 3 is the second pin from the right on the bottom row (Audio Out Left/Mono channel) Pin 4 is second from the right on the top row and is the ground or common terminal. (Pin2 top row first pin on the right is not used).
The SCART plug has a cable grip system which can be used to screw up and grip the body of the headphone socket. It may be necessary to wrap electrical tape around the body of the socket to increase its diameter so that it is gripped properly, but that is not always necessary. Once wired and re-assembled the very neat adapter can just be plugged into the SCART socket of TV, VCR, DVD or any SCART equipped unit. The SCART has a set volume which is not affected by the volume control of the TV. You can reduce the headphone volume using headphones which have their own control, and you can turn off or mute the main volume control of the TV itself, leaving your headphones unaffected.
If you have to use an ordinary headphone socket which is not pre-wired connect the socket so that the tip and the smaller ring behind it go to SCART Pin 1 and SCART Pin 3, with the larger ring at the rear connected to SCART pin 4. You can use ordinary wire, as the copper braid only has an effect over a long length of wire. You can also use any wire colour that you have. The pip is the Mono or Left Audio channel, whilst the ring behind teh tip is the Right Audio Channel.
If you are uncertain you will be able to look up SCART PINOUT on the internet and you will find diagrams you can follow.
If your SCART is in use on the TV you can get multiple SCART sockets for connecting a number of different SCART devices, and any spare socket on one of those can be used.