[FFmpeg-user] concatenating files in FFMPEG causing the wrong file length

[andrei ka]

you should join the dockerfile you're executing, i can't know what commands
you're executing and from where.
./configure is the conf command in ffmpeg src uncompressed dir, your
commands batch (shell or docker) is not located in that folder at
the time it issues the command, so, cd ffmpeg_unzipped_dir command is
missing or you cd-ed somewhere else meanwhile...

in a correct docker file all commands are ok for correct navigation b/w
folders (temporary or packages git trunks etc)

&rei