Video merge problem.

[Eden harim]

Hello, I've joined two mp4 files by using append function. I chose "copy" option for the video and audio.Then save as mp4 container.

The file was saved,but only the first of the two merged videos actually played after that vidoes stopped.however I can keep litening

audio without stopping. so I tried merging with another software but it seems like same problem. the information of two vidoes is   

matched (1920x1080, H264, ACC audio, 59.9fps). I don't wanna re-encoding because that consume too much times(almost 13 hours).

Could you guys help me to fix this problem?? or recommed other sofrware(even fee software) ??

thank you for reading! and sorry for my english grammer skills~!! I hope you understand well!