jimd - for video clips you need authoring software (if you want a lot of creative control) or a program such as ConvertXtoDVD.
ma1848ma - What is being used to convert the files? If it’s Nero, try something else (see notes to jimd above). Also, if it is Nero, it should be creating an error log. You can post the error log and we’ll be able to have a better idea of what is happening.