Is it possible to separate voice and background music from a video file.
I only need the background music.
Type of video: MP4
Working on Windows XP 32 bit SP3
Unless they're separate audio tracks in your video, not easily. What you'll probably have to do is extract the audio track from the video into a separate file, edit the audio file with a dedicated tool, then remux the result back into the video.
The demux/remux part is easy. What's going to be difficult is attempting to isolate the background music. You'll probably have to experiment with different effects, all of which will most likely result in either a significant loss of fidelity in the audio or not entirely removing the dialogue, if not both. What's more is that you're going to be re-encoding that output into a new mp3/aac file, and between the re-encoding and audio processing, your output is going to sound much worse than the original.
You may have better results by trying to re-master the background music and replacing the audio track in the movie file entirely.
I managed to remove background conversation/noise from a video by running a low-pass filter that was built in to the editor that I was using. The whirrs of my robot, which was the target of my video, remained.
Note that I am not an audio expert, and I cannot guarantee this will work for your particular case, but it's worth a try.