Hi there,
I'd be happy to help you! First off, Jav-It should automatically be doing this for you. So if your not seeing this behaviour, then clearly something is going on. Unfortunately, since you didn't really post any defails it will be hard to troubleshoot. So let me start off by asking the following:
1. What OS are you using?
2. If Windows, are you running the command line in Administrator Mode? (Do this if your not already doing so - It will remove permissions issues if you have any).
3. If your not doing so already, try omitting the "\" at the end of your output path. For example:
jav-it.exe download -c c:\temp\downloads\r18.com_cookies.txt -o c:\temp\downloads\done -i rbd00359
Where "c:\temp\downloads\done" is your output path where you want to save your videos to. To verify that downloading has started normally, check your output directory. You should see a file called "<content_id>.ts.partial" created, where "<content_id>" is the content ID of your video. Note: Depending on if your paths include spaces, you may need to add quotes around your path.
4. If your still not seeing your desired result, copy and paste the entire output of Jav-It to this thread so people can see what errors your actually getting.
5. If you download the first part successfully and for some reason it stops proceeding, you should have a valid *.ts file. If you start the download again using the exact same parameters, Jav-It will notice the first part is already downloaded and start working on the 2nd part.
Please give some of this a try and get back to me. With more information I can probably figure out what issues you have, and how I can prevent them in the future! (^_^);