The 30 day limit is set by default as a built-in safeguard against having a longer recording that results in an extremely large manifest that needs to be loaded into memory and will likely cause issues in a real world deployment. There are serious drawbacks to having such long recordings which is why we have set this limit. See recording length best practices.
You can extend the maximum recording time value by adding this property dvrMaximumRecordingLength to the /DVR/Properties section of Application.xml. The default is set to 108000 (30 hours). However, we strongly advise against increasing the recording length and playing back such a long recording.