Concatenated Video created with FFMPEG is longer than expected

Question

I am using this Video-List:

file 'C:\Users\X\Documents\test\input.mp4'
inpoint 00:00:02.7650000
outpoint 00:00:04.7650000

and the following Command:

ffmpeg -y -safe 0 -f concat -i output.txt -map 0:v -map 0:a -c:a copy -c:v copy output.mp4

which should result in a Video with 2 Seconds in Length. But if I do a check with ffprobe I get this:

Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'output.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf60.16.100
  Duration: 00:00:04.85, start: 0.000000, bitrate: 394 kb/s
  Stream #0:0[0x1](und): Video: h264 (High) (avc1 / 0x31637661), yuv420p(tv, bt709, progressive), 1920x1080 [SAR 1:1 DAR 16:9], 382 kb/s, 30 fps, 30 tbr, 15360 tbn (default)
    Metadata:
      handler_name    : VideoHandler
      vendor_id       : [0][0][0][0]
  Stream #0:1[0x2](und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 2 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
      vendor_id       : [0][0][0][0]

Whats the cause of this?

Answer 1

As explained in the documentation, the inpoint directive works best with intra frame codecs, because for non-intra frame ones you will usually get extra packets before the actual In point and the decoded content will most likely contain frames before In point too.

And it's the same problem for outpoint directive.