We have a difficulty to figure out what the problem is with the information you gave us. Does it played with software decoder? Please check it and do a test it with other device.
nPlayer Help - Decoder Setting(HW/SW)
In order to figure out the problem exactly, more detailed information is needed. And your sample file would help us. If you can, in order to test in the most similar conditions to those where you did, please upload your sample file to ftp://test.newin.co.kr or give us your file link to firstname.lastname@example.org.