With AviDemux, when saving you have to be careful to specify the output muxer and to choose a Video Codec and Audio Codec that are supported by the chosen format - otherwise you'll create a file that is unplayable (it won't stop you from doing so, so you have to double check everything before you set it running). These three settings are in the tabs on the left side of the main display.Well , we have been using Avidmux but it seems to crash or the files get corrupted. All we are doing is cutting and deleting segments then saving the video.