Depending on the camera model used, one could expand the recording time a 4GB file can take up by reducing the recording quality (compression, bit rate, resolution...) of your video.
With SOME cameras, you might be able to use an SDHC card forcibly formatted to a file system that does not have a 4G file size limit, eg exFAT or NTFS. If you can make it work, test THOROUGHLY.
Be aware that certain cameras also have a hard coded 30 minute video limit, which is there for reasons all unrelated to file size: In some markets, video cameras are taxed higher than still cameras, and the definition of a video camera in the relevant tax codes is continuous video recording capability beyond 30 minutes. In some cases, the camera might also not be THERMALLY designed to handle more than 30 minutes uninterrupted recording load.