How to sync background music with video ?

[AAC]

Over the weekend, I taped school girls folk dance video at the back of the school hall by consumer level camcorder. the HD video was good but I recorded all unwanted noise like coughing, laughing, talking by the internal microphone of the camcorder as well.
I have the original background music mp3 from the teacher but never success to sync the mp3 music with the movement of dancers, the timing is always wrong. Any tips to fix this problem ? I used Adobe Premiere Element 12 to edit it.

[Cornucopia]

Make sure your video clip includes ONLY from music start to music stop. Make sure that this music clip is the EXACT same version as the only that it is replacing (incl. no edits). Time them - they should amount to the same time. If not, they either aren't the EXACT same clip, or one is stretched/shrunk (aka pitch shifted, faster/slower tempo, time compression/expansion), or both, or one of the samplerates has been changed from what it was actually sampled as. If the first, edit one to match the other (depends on which can be edited). If the second, open the music clip in Audacity (or similar) and do [Effect | Change Speed] (or similar if in different editor). You'll probably have to make a few attempts (undoing in between) until you get the time just right. If the last, it would be hard to tell (maybe a little less so for us, but still) which was changed so your job will be difficult. If #3, you'll have to edit (almost blindly unless you are a good musician) first, then TC/E after - also quite difficult.

If success at changing, you should have no trouble syncing & replacing.

Scott

[AAC]

Thank you Scott again.
Yes, the MP3 was the original music source when dancing on stage. I will try it out by following your advice.
If I need to do more, say.... adding 30 seconds video of same group school girls dancing in the park with the same background music. How to merge this 30 second video seamlessly ?
Do you know any complete online video editing tutorial to learn from ?

[Cornucopia]

There are plenty of tutorials out there on the web. Which one will work for you, I can't say.
What do you consider seamless? Can you do fit-to-fill? It could be workably done.

For editing, use an editor. APE should be able to do all of that (except maybe the audio TC/E).

Scott

[AAC]

Yes, you are right. there are tons of video tutorial on YouTube. What I need is series video production tutorial to learn step by step in my own pace. I want to do more multi-camera or one camera in different locations music video shooting and editing, in future.