How to crop a video

[flash_22]

hello,
I'm trying to crop a video (mp4). I adjusted the video and audio output to "Copy" because I want to crop without reencoding, because I 've got many videos.
After setting the crop in avidemux the resolution is shown: 1024 x 576 => 1024 x 434. After saving the file in windows explorer I see two strange things:
1) the file size isn't smaller
2) the resolution is still 1024 x 576 and not 1024 x 434.

And when I check "Play filtered" in avidemux the black bars are shown.

What are I'm doing wrong?

[Jan Gruuthuse]

If you want to resize video, you can't use for video: Copy. You need re-encoding the video.
Set Video Output to Mpeg4 AVC and Output Format to MP4v2 Muxer.