Hi, I had same challenge to start with an empty DRV folder, with live streaming every time.
I do it with a cronjob, so you can easily schedule, the api function and erase the folder at any moment you want.
because the delete function, curl -X DELETE, for DVR by api wasn't available for a long time, I used the update function for dvr (-X PUT -H)
here a little example:
Update the DVR settings to a different path
* 6 * * 1 /usr/bin/curl -X PUT -H 'Content-Type: application/json' -d '{"application":"application-name","stream":"stream-name","path":"/path-to-original-folder
* 6 * * 2 /usr/bin/curl -X PUT -H 'Content-Type: application/json' -d '{"application":"application-name","stream":"stream-name","path":"/path-to-second-folder
* 6 * * 3 /usr/bin/curl -X PUT -H 'Content-Type: application/json' -d '{"application":"application-name","stream":"stream-name","path":"/path-to-third-folder
* 6 * * 4 /usr/bin/curl -X PUT -H 'Content-Type: application/json' -d '{"application":"application-name","stream":"stream-name","path":"/path-to-original-folder
etc
* 5* * 1 rm -rf //dvr-path-to-original-folder/* (delete dvr folder at monday 5am)
* 5* * 2 rm -rf //dvr-path-to-second-folder/* (delete dvr folder at tuesday 5am)
* 5* * 3 rm -rf //dvr-path-to-third-folder/* (delete dvr folder at wednesday 5am)
* 5* * 4 rm -rf //dvr-path-to-original-folder/* (delete dvr folder at thursday 5am)
etc.