How to change encoder metadata in mp4

[psycholyzern]

I encoded a video using HandBrakeCLI..
it went great.. but I have a problem.. when I checked with ffmpeg, there will be a line:

encoder : HandBrake 0.9.8 2012091600

I tried this:

ffmpeg -i abc.mp4 -metadata encoder="GM" -acodec copy -vcodec copy abcd.mp4

but when I check the output:

encoder : Lavf55.7.100

is there any mistake I did?
how can I change the "encoder" to something else or remove it??

[Baldrick]

I changed the thread title so it better describes your problem.

No, I have no idea how to change the encoder metadata.

[psycholyzern]

Im sorry about the title..

Im still waiting for best answer

[El Heggunte]

Use a hex editor and overwrite the offending string with spaces, interrogation marks, or asterisks.

[psycholyzern]

hex editor?? seriously???
how to do that in terminal??