It appears that .ced files are saved on SD card in JVC digital cameras in cases when the card itself is formatted with unsupported or wrong file system. In any case, a .ced file seems to be just few kilobytes in size and is likely index or contains just some metadata so there is really no way how to convert it, or recover it to a video file (for example as MP4 file).
Some users had some success with importing .ced file in iMovie for Mac. However, this may be due the fact that actual video track (.mts, .mod) was also recorded along the .ced files. This means that iMovie just used the .ced file as a link to the actual video recording and could import it. But in majority of cases, only .ced file is present and no video track so no import or conversion is possible.