Non-monotonous DTS in output stream when concat videos using ffmpeg

Question

I have three videos which I want to concat together the problem it works fine for some videos but when I test a specific video it gives me an error and cause the resulting video to show in a strange way and everything is moving very fast in the video like I was forward up the video
this the code I used to add the video together from a file this the out.txt

file 'D:/Build/start.mp4'
file 'D:/Build/a.mp4'
file 'D:/Build/Song & Lyrics/2f.mp4'

the command i used with ffmpeg

ffmpeg -f concat -safe 0 -i out.txt -c copy -y go.mp4

i faced this error

    [mov,mp4,m4a,3gp,3g2,mj2 @ 05c0dbc0] Auto-inserting h264_mp4toannexb bitstream filter
Input #0, concat, from 'out.txt':
  Duration: N/A, start: 0.000000, bitrate: 280 kb/s
    Stream #0:0(und): Video: h264 (Main) (avc1 / 0x31637661), yuv420p(tv, bt709), 1280x720 [SAR 1:1 DAR 16:9], 155 kb/s, 29.97 fps, 29.97 tbr, 90k tbn, 59.94 tbc
    Metadata:
      creation_time   : 2018-02-08T13:25:49.000000Z
      handler_name    : ISO Media file produced by Google Inc. Created on: 02/08/2018.
    Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 125 kb/s
    Metadata:
      creation_time   : 2018-02-08T13:25:49.000000Z
      handler_name    : ISO Media file produced by Google Inc. Created on: 02/08/2018.
Output #0, mp4, to 'go.mp4':
  Metadata:
    encoder         : Lavf58.7.100
    Stream #0:0(und): Video: h264 (Main) (avc1 / 0x31637661), yuv420p(tv, bt709), 1280x720 [SAR 1:1 DAR 16:9], q=2-31, 155 kb/s, 29.97 fps, 29.97 tbr, 90k tbn, 90k tbc
    Metadata:
      creation_time   : 2018-02-08T13:25:49.000000Z
      handler_name    : ISO Media file produced by Google Inc. Created on: 02/08/2018.
    Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 125 kb/s
    Metadata:
      creation_time   : 2018-02-08T13:25:49.000000Z
      handler_name    : ISO Media file produced by Google Inc. Created on: 02/08/2018.
Stream mapping:
  Stream #0:0 -> #0:0 (copy)
  Stream #0:1 -> #0:1 (copy)
Press [q] to stop, [?] for help
[mov,mp4,m4a,3gp,3g2,mj2 @ 05c38840] Auto-inserting h264_mp4toannexb bitstream filter
[mp4 @ 061b8f00] Non-monotonous DTS in output stream 0:0; previous: 624624, current: 88735; changing to 624625. This may result in incorrect timestamps in the output file.
[mp4 @ 061b8f00] Non-monotonous DTS in output stream 0:0; previous: 624625, current: 89247; changing to 624626. This may result in incorrect timestamps in the output file.
[mp4 @ 061b8f00] Non-monotonous DTS in output stream 0:0; previous: 624626, current: 89759; changing to 624627. This may result in incorrect timestamps in the output file.
.....

[mov,mp4,m4a,3gp,3g2,mj2 @ 05c38840] Auto-inserting h264_mp4toannexb   bitstream filtereed=69.7x
frame= 8991 fps=2903 q=-1.0 Lsize=    8378kB time=00:05:58.22 bitrate= 191.6kbits/s speed= 116x
video:2469kB audio:5625kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 3.500685%

so what the problem make this error. the problem appear when i use this new start.mp4 to be merge with my videos i tried on other ones and it worked fine.
Update
i tested to convert the videos to MTS formate then concate them as an answer to similar problem but the problem is when i convert the mp4 videos to this formate the size of the file be too large from 6 MB to 42 MB!! so if there is a better answer. or a way to make the file still same size or less the linke of the answer is here but it worked fine Thanks in advance

Answer 1

on this time I tried to solve the problem and make some searches and I notice that the first video does not have the same frame/second as the other videos I tested before and I use this command to make them all have the 25 frames/sec

FFmpeg -y -i source.mp4 -r 25 -s 160x90 -c:v libx264 -b:v 3M -strict -2 -movflags fast start destination.mp4

this command I make all video with same frame/sec and resolution when I start adding the outputted videos it output without any problem so I need a confirmation if this information is right as iam not sure. but it worked for me