When editing in Nero Video, if the source clips are 4K resolution or higher, and you would like to have the output file also in 4K, please
1. Open Options -> Movie Options, select the Resolution option as UItra HD (4K).
2. For better preview quality, click the Preview Quality setting under Preview area, drag the marker to the rightest.
Please notice only configure Movie Option to 4K when the source clips are 4K resolution or higher.
If the source clips are in small resolution, the output files will not be in good quality even though Movie Option is 4K.