Mannn I have the same problem as you, one of my teachers has been so useless regarding media language section, like honestly the worst!
From looking at previous exam answers and looking at an A2 media revision pack (
http://www.slideshare.net/andywallis/a2-media-studies-revision-pack), media language is in reference to how you (the producer) have created meaning using mise-en-scene, cinematography, editing and sound.
You can pretty much use any of the theorists from the other sections and apply them to media language. So, for example, 'the final girl' theory proposed by Carol Clover can be applied to media language (I created a horror trailer, unfortunately I do not know any of the theorists for music videos!)
Example - For my A2 coursework, I produced a horror trailer. I have constructed meaning by using a female protagonist 'Taylor', and have constructed her to appear kind, caring and feminine at the beginning of the trailer, but have developed her psychotic, masculine change towards the end. This complies with the 'final girl' theory, proposed by Carol Clover, as she suggested that a female character in horror trailers undergoes a change from highly feminine to masculine as the narrative develops. At the beginning, I used high key lighting to give connotations of her angelic presence, along with her costume consisting of a blue floral top, her long hair flowing down her back, and make-up such as mascara and foundation to portray her femininity. Towards the end, she is seen in a close-ups with her hair tied back behind her face, demonstrating connotations of a typical male hair-cut, she is turning masculine.
Hope this helps! (Also, if I am incorrect, feel free to correct me!)