File size collapses to zero on opening file

[Clafoutis]

Hello!

I made an application driving VLC to capture video streams to files (using command lines, on Macintosh). This works fine, the resulting files are ok.

But when I double-click the file (my application being closed, has nothing to do with this) , launching an instance of VLC to read the file, the size of the file collapses to zero byte, and then my video is lost forever... This happens not always, seemingly on bigger files ( >2GB).
Sometimes, I avoided the problem by duplicating the file before opening it, but I cannot say it works anytime.
Has somebody encoutered this problem ? Is there a way to eliminate forever this erasing ?

Thousand thanks for helping me!
(please pardon my incorrect english)