H.264 Alarm Recording

Hi John, We are security consultants based in the Gulf region, and have just installed a VMS on one of our projects. For the moment I would prefer not to name them as it is quite a delicate subject as the VMS has been specified on other projects and there could be issues. What we were looking to achieve on the project was that certain cameras would record at low frame rates such as 1fps or 5fps and then on an alarm activation or certain designated access control events, recording would increase to 25fps for a set period of time. We have had a number of discussions about this requireent with both the integrator and the manufacturer. From what they are saying for H.264 recording it is either 1fps or 25fps. I have never come across this before and I am wondering whether it is a limitation in the VMS rather than H.264. I have copied an extract from an e-mail from the manufacturer below and I wondering what your thoughts on it are. Many thanks John Manufacturer: You are also correct in assuming that you can set your perimeter cameras to recording 1fps and go to 25fps on alarm. But, you are not correct in assuming you can go from 5fps to 25fps. As I have mentioned on our previous email, the h.264 technology does not allow you to go from 5fps to 25fps. This is not an efficient use of the recording algorithm as there are no "B" frames. You can record either 1fps and go to 25fps, or record at 25fps constantly using the equipment and firmware that you are using. Because the h.264 algorithm is much better than MPEG at saving recording space, you can get comparable recording periods by using full 25fps recording instead of dropping to 5fps. Also because you can change the bitrate on all individual cameras, you can tweak each cameras recording quality to allow you to fit exactly onto the storage you have , for the retention period you require.
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