Are you having trouble uploading video evidence files that are too large?
There are many factors that affect the size of a movie or film file but the main issue is usually the resolution that the film was recorded in.
HD or 4k formats are commonplace on many modern mobile phones but this leads to large file sizes. Before you start recording your evidence, check that you're only recording at a maximum resolution of 720p.
If the recording has already been made, or if it is just too large, then you can use software to further reduce the resolution and to chop the film into several files. e.g. Part 1, Part 2, etc.