i cant't upload videos of my computer and i think it is due to

Directory Permission
Permission Check failed Directories listed below are not writable.
jVideoDirect fetch and transcode video using background process.
As a result, these directories are needed to be accessible by the username of your webserver.
Typically, apache or nobody.

You should check
1. Directory and sub-directories of (joomla root /jMediaDirect) are owned by the username of apache
OR
2. Directory and sub-directories of (joomla root /jMediaDirect) are set with permission 777.

Otherwise, jVideoDirect will not working correctly.

If you have RECURSIVELY set their permission OR changed their owner and failed, your php path must be incorrect.
joomla root / jMediaDirect
Not Writeable
joomla root / jMediaDirect/videos
Not Writeable
joomla root / jMediaDirect/videos/tester
Not Writeable
joomla root / jMediaDirect/videos/temp
Not Writeable
joomla root / jMediaDirect/videos/pics
Not Writeable
joomla root / jMediaDirect/videos/pics/small
Not Writeable
joomla root / jMediaDirect/videos/pics/medium
Not Writeable
joomla root / jMediaDirect/videos/pics/small2
Not Writeable
joomla root / jMediaDirect/videos/org
Not Writeable
joomla root / jMediaDirect/videos/hd
Not Writeable
joomla root / jMediaDirect/videos/sd
Not Writeable
joomla root / jMediaDirect/videos/csv
Not Writeable
joomla root / jMediaDirect/buffer
Not Writeable
Background Process
Absolute Path to PHP Present
Background Processing failed Please check "PHP Path" and/or "Double check Directory Permission of (joomla root / jvideodirect) and/or availability of "exec()" function.

please help me!!! i'm alrready put permissions 777 for every archives in jMediaDirect

are you using the latest version 1.1 RC3A ?

I too have the same problem. how to solve

check server permissions and configuration, otherwise consult with your host.