[FFmpeg-user] issue with concat and seek

[Carles Vila]

Hi, I have two mp4 (myIntro.mp4 and movie.mp4) that I want to concatenate,
but the second video should start at 10 seconds.
Both mp4 have same properties.

Normal concat without seeking works just fine:
ffmpeg -f concat -i list.txt -c copy output.mp4


I cut the first few seconds of the movie to remove some logos using:
ffmpeg -ss 10.1 -i input_2.mp4 -c copy input_2_nologos.mp4

Playing back this file works as expected, the logos are gone.

Problem is when I repeat the concat command above with the new movie,
obviously updating the list.txt file,
The logos are back! What am I doing wrong? Are the logos preserved, only
hidden when seeking?
Can I do the concat and seeking in one step?
Thanks for any hint