Newbie to video Editing

[jrws]

I hope this is the right forum as I cannot find a more appropriate one.
I have been using AviDemux as recommened by some friends of mine but I am having troubles using it correctly. I have an MP4 that I needed to edit:
- crop the edges to get rid of bits that don't need to be there
-Remove 2s of audio from begining and end

So I googled and youTubed the tutorials on how to do that, and I was able to. But, for some reason even though it works fine in AviDemux, when the video is viewed in any other player it is one of two things: Out of sync (voice .1s too slow) or it is speed up unbelivably fast about 4x.
I cannot figure out what is wrong and I need some help as this is a project I need to complete. I have tried saving with all the combinations MPEG(x-vid) + Lame + avi, ect.
If someone could quickly explain codecs, it would be helpful.

Thanks.

[Jan Gruuthuse]

Telling you have an MP4 is not enough, that is a container (box) within it a Video with Audio track(s) each encoded with a specific codec.
Guide to encoding types
On the left of that page under the heading: General information, you find some more info.
What avidemux are you using: 2.5.4, 2.5.5 or 2.5.6 on what OS? In any other player? Does this mean software player on the computer? Where should the video play on: dvd, stand alone player, ... ?
You need to extract/export the audio. Cut the audio 2 seconds in front and end in audio editor like Audacity. Create 2 seconds of silence in same audio editor and save this as .wav or .mp3. Then you can paste this in front and end of the cut audio. this can not be done in 2.6.

[jrws]

Thank you for your help, I will try your suggestion. If I understand correctly I need to get Audacity and extract the audio from the MP4 original, and then using Audacity edit the audio adding 2s silence in front and back. How do I extract the audio? Is audacity able to do this automatically or do I use a different program?
I am using Windows 7 and 2.5 of Avidemux. I used Windows Media player to view the edited video as well as VLC player. While the Avidemux viewer seems to see it at normal speed. The video will eventually be uploaded to youTube.

[Jan Gruuthuse]

read the remarks made by styrol to in the second posting of this thread to