App for separating sound

Does the video already exist and you need to split different sounds from the audio track? Recorded with a phone, video camera, or similar? If so, then it's not a straightforward process and the result will depend on several factors, like the relative volume of the different sounds and the overlap of frequencies. It can never be perfect just due to the nature of sound.

I don't really deal with audio much, but the basic process is going to be to extract the frequency bands where most speech is (kind of like adjusting an equalizer to extreme measures), but you're going to get the speaker's voice mixed with the singer's voice from the music (if there are vocals). Also the audio bands outside the vocal range where you take the music from will be missing a pretty large range of sound from the vocal range, so it will probably sound muffled and distorted. But if you don't need perfect quality and are just interested in mostly isolating the two, you can try Audacity and follow these instructions.

You might have to extract the audio from the video using a different program before loading it in Audacity. I'm not really sure though.