I would add more details to the question is hard to say what is exactly Your problem. However, from mentioning mp4 container I guess You are talking about cellphone or some IPhone like stuff...
Try using MediaCoder - it has simplified and easy to use GUI for video conversion. Latest versions for sure allow non-problematic converting to mp4. Though I suggest also trying older 0.3.7 version (different advanced setting configuration).
When converting go to the tab %26quot;picture%26quot; - select desired size (You might need to check what resolutions are acceptable by Your device, player).
Most of wizard type converters have already set size of video specified for exact device.|||You should be able to change the display/size of the clip you are about to convert, it depends on your converter. I use SUPER, which is an excellent converter, and you have a big choice in what resolution you want to convert it to.
