Any clue why this trick to mute shutter sound won't work for video

[TimeTraveler7]

I've tried this trick...
iPhone: Disable Camera Shutter Sound ? Technipages
for changing the sound file in /System/Library/Audio/UISounds to an empty/dummy file, and it works fine for taking photos without any shutter noise.
However, when I tried the same recipe for video sounds (i.e. replacing begin_record.caf, begin_video_record.caf, end_record.caf, end_video_record.caf with empty/dummy files), it wouldn't work. The video portion of the camera would simply not start recording at all.
Any idea what went wrong?