h.264 splitting & merging

Hi Transcode-Users!

I'm very new to transcode. I want to develop an app which splits parts out of multiple video files an merges them afterwards to one movie. The movie files are encodes with a special h.264-codec which is optimized for security-cameras. Each file contains 1 minute of video at 5 fps = 300 frames. I did some experiments with avisplit, but the accurancy was not very good, I think this is due to the strange codec. Avimerge worked fine.

My questions:
-Is it overall the right approach to handle this use-case?
-How can I get a better accurancy in splitting my video? Maybe converting in another format before splitting?
-How can I convert my 5 fps-movie to 25 fps? I tried fpsmod, but transcode never stopped running?!

Thank you for your help!
Chris