Is it possible to add a short "neutral sequence" (=short sequence of black -or white- stable image) at the begining or at the end of a video track with a command line program (ffmpeg, MEncoder, mkvtoolnix collection or other) ?
I am looking for the video equivalent of the "pad" parameter of the sox audio editor but would accept a more complex procedure.

Notice that creating a "neutral sequence" with
ffmpeg -i {original file} -t {some seconds} -vf "fade=t=int=600:d=0.5" {neutral sequence}
is not a satisfactory solution because the {neutral sequence} may not be concatenated to the {original file} because the caracteristics (codec,...) of the created {neutral sequence} usually differ from those of the {original file}.