Is this related to your other thread?
If you are asking it it would be possible to power a bluetooth transmitter directly from the headphone output of an iPod the answer is no. Even if the iPod could deliver enough power in principle (there are dedicated headphone amps that probably could) that is irrelveant; the waveform (=the music) is not suitable for powering active devices.
Thanks yeah they are related, just out of interest why wouldn't the waveform be suitable for powering active devices? so would there be no way of powering any electrical device through the headphone socket?