I have been looking at some new cars and while many cars seem to have an auxilliary plug-in adapter, some cars claim they also have MP3 playback. When you see the information in one of the car brochures, they seem to be different things but if you have an iPod for example, would you not just plug it into the adapter? Are the vehicles which claim MP3 playback talking about something else in addition to the plug-in auxilliary?

My after market car stereo is a Clarion. The CD player can play MP3's / WMA files that are recorded to CD. (Think MIX tape that holds 135 songs). It also has a RCA Left/ Right jack in the back that you can plug a RCA to Headphone jack adapter cable into and use the source button to select for plugging in a MP3 player or iPod.

I have a GM vehicle with a MP3 playback compatible CD player.

Burn MP3s to CD and play 'em in the car. I can also buy an iPod adapter that allows the factory head unit to control the iPod.

My wife's new Honda has an aux input so she can plug in her satellite radio or mp3 player. The CD potion of the built-in radio can also play mp3s burnt to a CD.

Some decks like my Pioneer DEh-7900BT don't have an auxilliary input. They have an ipod interface at the back of the unit. When installing it, you connect the (not included) cable and route it to your glove compartment where you plug in your ipod. This is not as convenient as just plugging in an audio jack on the front, but it actually allows you to control the ipod from the head unit itself.

I just got a new ipod nano (the fatty nano) and it doesn't work with my car adapter (which plugs from the ipod dock connector into my factory head unit).

This is not good. :(

I've read that it looks like Apple has re-mapped some of the pins on the dock connector - the video out doesn't work as it did on the old ones either.