Well, your question is very general! As I understand and based on my experience,
I suggest you something:
1- First and most efficient is that you can analysis your data online then extract your statistics and keep your results.
Easy for research here: http://www.mathworks.com/help/images/examples/detecting-cars-in-a-video-of-traffic.html
2- You can tag your data and keep only the sequences that you need, at least ignore a big unnecessary data automatically.
3- If you need to keep the video sequences for any reasons, then I suggest to use video compressors and decrease your videos not only by compressors also in terms of size.
http://video-compressor.en.softonic.com/
solved how to capture road traffic data for a specific period and place