Still confused....lol Output codec has got me lost. I opened it in avidemux......i see a big green screen, have no clue what to do from there
Video files are 'wrapped' in a format such as avi, mpg, mp4, mkv and so on.
In side the wrapper is the video which has been encoded using some codec (examples MPEG-4 AVC (H264), FFV etc) , usually with an audio track or two which itself uses some specific audio codec (MP3, AAC, Vorbis, AC3 etc).
To get some idea about what your files actually are, I suggest you install MediaInfo from the repository, which should (in KDE) give a right click menu entry to open a media file using MediaInfo. You should then be presented with the info about the file.
There is also a command line version of mediainfo ..... and this gives much more info about the file, but is not normally required for general information.
With Avidemux, if the video and audio codecs are what you wish, then you can change the wrapper format simply by copying both audio and video and selecting the format at the bottom. It should complete very quickly. If you need to recode the stream then it will take much longer of course.