Shareaza

I can simply say KMPlayer is the best player to preview incompleted downloads.

The problem is that sometimes it damages video file when reads incompletes directly. I don't know the reason and I'm not even sure that its the KMPlayer destroying the files.

What I experienced was that my downloads changed to 0% and noticed that happened right after previewing them with KMPlayer.

The most obvious cause would be it recognizing the correct file type and changing the extension to match, which would hide the file from Shareaza. Alternately it could remove the "corrupted" parts making the partial unusable for Shareaza.

You know that KMPlayer does these thing by its own?

No, I don't. I know nothing whatsoever about KMplayer. But if playing something in KMplayer hides it from Shareaza those are the obvious things to check for.

Extension renaming is not the case. if it was it may would happen for all files.

Probably so yes. How often does this happen and is there any kind of pattern? And do you have Shareaza running when watching partials? That might cause a file error...

Yes Shareaza is running.

if KM changes a part of a file, Shareaza should just redownload that part.

My first thought was that somehow KM and Raza try to access one part at the same time and windows prevents Shareaza from writing.

It is not really about accessing the same part. It is about trying to open a file that somebody (KMplayer) has open for read access for write access. This creates a file error and makes Shareaza lose the partial. You should always create a temporary copy and preview that if Shareaza is running. Making a batch file or executable that does that for you automatically when trying to open a .partial should be simple enough...

Opening file by both programs should not generate file error in Shareaza normally. Damage only happens in rare occasions for an unknown reason.

It would only happen if Shareaza tries to open the file for writing while KMplayer has it open for reading. So it would not happen every time you do a preview.

I thought Shareaza opens files on start.

It is generally a bad programming practice to have files open unless you are using them. This should be especially true for a P2P application that was originally designed to work with Windows 9x. So I'd assume Shareaza closes files it is not using...