By hearing the audio I found that it is an image encoded by SSTV (Secure Slow Television) Slow Scan television is a picture transmission method used mainly by amateur radio operators, to transmit and receive static pictures via radio in monochrome or color(copied from WikiPedia). But it is quite possible and easy to decode. Decoding it with [This Tool](http://users.belgacom.net/hamradio/rxsstv.htm) will give us the flag in the following image.


Flag : ```rgbCTF{s10w_2c4n_1s_7h3_W4V3}```