user2813: I would like to connect arduino mini pro to mini jack output and send sound through it.
What would I need here, how can I connect the mini jack to arduino and how to send data of sounds (any library?) to that connected output?
EDIT
The sound source will be a music file ( streamed via bluetooth). I would like to be able to connect this output to a speaker and play (stream) music via bluetooth.
EDIT
Either mono or stereo will be good for me. My plan is to: stream the music via bluetooth to bluetooth module (for now I think about HC-06), send that data stream through arduino mini pro to the output mini jack. 
Do I need in that case some kind of mp3/other format decoder module like VS1003B on ebay ?

user19409: The Arduino Uno / Mini Pro is not really the right tool for the job. It has no native audio output such as a 3.5mm jack.
Having said that I am sure it can be done - but it won't be the best quality sound. I have no doubt that it can be achieved with one of the following methods:

using the tone() function.
by using a R-2R resistor ladder network and some sort of amplification circuit.

The Arduino Due and the Arduino M0 / M0 Pro both have inbuilt DAC's, meaning that they can output analog signals which can be used to drive a speaker circuit.
Another option is to use a Raspberry Pi which has a native 3.5mm audio jack.

2813: <p>I would like to connect arduino mini pro to mini jack output and send sound through it.</p>

<p>What would I need here, how can I connect the mini jack to arduino and how to send data of sounds (any library?) to that connected output?</p>

<p><strong>EDIT</strong></p>

<p>The sound source will be a music file ( streamed via bluetooth). I would like to be able to connect this output to a speaker and play (stream) music via bluetooth.</p>

<p><strong>EDIT</strong></p>

<p>Either mono or stereo will be good for me. My plan is to: stream the music via bluetooth to bluetooth module (for now I think about HC-06), send that data stream through arduino mini pro to the output mini jack. </p>

<p>Do I need in that case some kind of mp3/other format decoder module like <a href="http://www.ebay.com/itm/VS1003B-MP3-Decoder-Module-Development-Board-STM32-Contains-Microphone-/121315052297?pt=LH_DefaultDomain_0&amp;hash=item1c3ef0cb09" rel="nofollow">VS1003B on ebay</a> ?</p>
 19409: <p>The Arduino Uno / Mini Pro is not really the right tool for the job. It has no native audio output such as a 3.5mm jack.</p>

<p>Having said that I am sure it can be done - but it won't be the best quality sound. I have no doubt that it can be achieved with one of the following methods:</p>

<ul>
<li>using the <a href="https://www.arduino.cc/en/Reference/Tone" rel="nofollow noreferrer"><code>tone()</code></a> function.</li>
<li>by using a <a href="https://en.wikipedia.org/wiki/Resistor_ladder" rel="nofollow noreferrer">R-2R resistor ladder network</a> and some sort of amplification circuit.</li>
</ul>

<p>The <a href="https://store.arduino.cc/usa/arduino-due" rel="nofollow noreferrer">Arduino Due</a> and the <a href="https://store.arduino.cc/usa/arduino-m0" rel="nofollow noreferrer">Arduino M0</a> / <a href="https://store.arduino.cc/usa/arduino-m0-pro" rel="nofollow noreferrer">M0 Pro</a> both have inbuilt DAC's, meaning that they can output analog signals which can be used to drive a speaker circuit.</p>

<p>Another option is to use a Raspberry Pi which has a native 3.5mm audio jack.</p>
