or http://avidemux.org/ and its forum.
http://avidemux.sourceforge.net/download.html
First of all, i have to say that al programs i find on http://sourceforge.net/ are cool programs, and are Open Source Software and i think they are all free.
Avidemux is easy to use and can not only convert files to another format but is also fast to cut pieces of Avi files (avi, flv, mpeg...).
To edit a movie you just go to File menu and select open, or just drag the video to middle window of avidemux.
To cut a piece of movie just stop video where you want to set beginning and press on:
You can also go to menu bar, Edit and choose: Set Marker A.
Next you keep playing video till the choosen end point and press Stop, or drag the "play" bar till the choosen end point. And then you just go to Edit, Set Marker B, or press on:
And finally go to File menu, and select Save.
I just explained how to easily cut a video but you can do many other things with Avidemux :)
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If we want to save our video without sound we have to go to Audio Menu, Select Track and uncheck the selected audio track:
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Some image about encoding options:
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Another software i have used in the past for video editing or converting video and audio to another codec, is:
To just edit audio:
And there was another software i used sometimes for cutting video files that was called MP4Box and now seems to be called GPAC: https://gpac.wp.mines-telecom.fr/downloads/gpac-nightly-builds/
For Windows i used My-MP4Box-Gui, and you can find it on videohelp.com site (the developpers site is down, author Matt Bodin): http://www.videohelp.com/software/My-MP4Box-GUI
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Site with many links to video/audio editing tools (site that has been online maybe for more than 15 years now and where i used to look for dvd ripping tools):