Welcome to justanswer
There are three image qualities available on canon SX 50 HS
You can have the frame rate of 24 and 30 fps in HD mode
and 30 fps for standard definition also
To change the image quality settings, press "FUNC SET" button
then choose  for 24 fps in HD mode
or  for 30 fps in HD mode
or  for 30 fps standard definition mode.
Sorry but you can only set the frame rate to only the rates that are given by the canon. There is no manual setting of frame rate speed.
This is a Canon issue and this is the way it is. So you cannot get a 25 fps rate.
Is there anything else I can help you with.
Please revert if you need any assistance and don't forget to rate the chat. Regards Nathan.
Thanks mate. I wish i could have been a real help. Anyways if you are satisfied please rate the chat.