Sound and music techniques in the 'Hollyoaks' clip

A lot of ambient sounds are use in this excerpt to support the setting which is a forest. Bird voices help to create the natural sounds and when he's walking you can hear leaves. It is a kind of versimilitude, creating a sense of reality. To the same time you can hear the heavy breathing from the guy, this one is called amplified sound. After he says the first time "Tom" the music begins. The trumpets are non diegetic sounds. The music becomes stronger to reflect his fear to the audience.
When he jumps into the water we can hear and see it, so the water noise is a diegetic sound. In the time, where he is in the water the music increases until the moment he recognize that the jacket is not his son.
Under water you can hear his sound perspective.(But 0:25 you can hear bird voices) The point of view is changing between the man and woman, so the sound perspective is changing too.
Then when he emerges the music stops, so that the audience can listen to the dialouge.
Another diegetic sound is the bang against the window and the screaming from the inside of the car. It is isolated, because the audience see the car also from the outside.
After this you can hear again the ambient sounds (birds) and the diegetic sounds (water; screaming from the guy). When he's under water again the song from Snow Patrol ("The Finish Line") begins. It shows that the men give up or loses his fight against the water. His power is gone and maybe he dies because of this. There is a smooth transition between his bubbles sound and the song. The song match to the slow motions of the guy.
When the camere isn't showing him under water is the song still playing and all the ambience and diegetic sounds are disappeard.
It is very synchronous, because the song supports the action very well, it shows the importance of this what is going on. This little moment could change everything. Through the music and sound the audience can feel the emotions and maybe can develop own emotions too.