Concatenate video in ffmpeg -> time stamps problem

[nsenada]

Hi

I have a complete audio recording of a concert and a video that is missing the first few minutes. I want to create a complete video file, which begins with the audio and a still image, then switches to the video seamlessly. I don't want to re-encode the video footage.

The video is in .mov format, H264-MPEG-4 AVC (part 10) (avc1) with MPEG AAC Audio.

I created the beginning (audio+still image) with the same video specs using Shotcut, then tried to concatenate the two using

ffmpeg -f concat - safe 0 -i files.txt -c copy Output.MOV

but I got the lots of these error messages:

84, current: 15880499; changing to 16086485. This may result in incorrect timestamps in the output file.
[mov @ 0x55b9e0253500] Non-monotonous DTS in output stream 0:0; previous: 16086485, current: 15881139; changing to 16086486. This may result in incorrect timestamps in the output file.

and the output video has the incorrect speed.

Can anybody help me out with this?

EDIT
Nevermind, I just solved the problem by remuxing .mov into .mkv