If you have added some media files, movies or songs, your music app or gallery wont show the newly added files until something called Media scanning has done. Some firmware’s will begin media scanning right after you copy media files to your SD card, but some wont. So, When your reboot your phone, media scanner will automatically run on the start-up and new files will be cached by the applications and it will be listed.
But rebooting the device every time you added one or two files is time consuming and does not seems to be a great way. How to run media scanner manually?. There are few free apps in the android market to run media scanner manually. These apps generally need no root access.. Some of them are,
How to Start media scanner manually using Rescan Media
For CyanogenMod users, no application is needed to manually run media scanner. You should possibly have “Dev Tools” in menu. Open it, scroll down to find ‘Media Scanner’. Tap it to begin scanning.