"avidemux" is a very good free converter and basic editor(cut, join, filters). It supports most video input formats like avi, mov, wmv, asf, mkv, mp4, flv, vob, mpg and can convert to many video formats like avi xvid, avi-dv, mpg, mp4 h264, flv. This is a very basic guide to get you started with avidemux.
::Open And Join::
Open your video file. You can also join files by choose File->Append(Note that video clip must have same width, height, framerate or else wont it work). If you are opening a DVD then choose the VTS_01_1.vob(the main video might be under a different number so you migh try different VTS_XX_01.vob) and all vobs will automatically be imported. Select Yes if you want index images.
If you want to cut then drag the bar at the bottom and click on A to set the start and B to the end. You can also delete parts like for example commercials, set the A and B and press delete on your keyboard.
If you want to convert to VCD, SVCD, DVD, PSP, IpoD or FLV then choose Auto in the menu and select the format and avidemux will automatically change all settings for you.
If you want to convert to an another format then choose the video and audio codec under video and audio. Like H264, Xvid, DV, MJPEG, Huffyuv. If you just want to cut or join video then change to Copy under video and Audio.
::Custom output file size::
If you want to convert to a custom file size then click on Tools->Calculator, choose AVI, set the file size, set the audio bitrate(128-192kbit/s is good for most stuff) and avidemux will automatically set the video bitrate so the output file size size will be correct.
You can also add video filters like Resize, Black borders, Color adjustments, Sharpness, Subtitles(srt,ass/ssa,sub), Deinterlacing. Just click on Filter under Video to add the filters you want to use.
Select the output container Format like AVI, MPEG, MP4, MKV, FLV. If you are making DV, XviD, Huffyuv video use AVI. If H264 video use MP4 or MKV. If MPG(VCD,DVD) use MPEG-PS(A+V).
Select Output at the top middle to preview the video, like for example look so the resolution/size and black borders look correct.
Last save the file, avidemux wont automatically add the extension like .avi so name your file with the extension like video.avi , video.mpg, video.mp4, etc.