How to get rid of the dialogue in the movie and keep only the background music?

first of all, it is absolutely impossible to eliminate human voices with mono.

It's best to find a software that can extract the sound of video in stereo. Then edit it with cool edit pro 2. audio editing software.

open Cool Edit, then open an audio file, and then click edit-select all waves. Then select "transform"-"waveform amplitude"-"channel mixer"

select "Vocal Cut" at "preset" and "new left channel, new right channel" at the left of the picture

to carry out relevant tuning.

Then you can click "Preview" to audition,

During the audition, you can also adjust the effect.

After the experiment of "new left channel and new right channel", you can only make the human voice appear in the left channel or right channel.

After the adjustment effect is satisfactory, click OK ~ ~ to save ~ ~ ~, and an audio file with human voice eliminated will be done!