I found that my MBP is out of space almost all the time. Using GrandPerspective (Free), I found that most of my space were taken by uncompressed movie files (simulation movies). Thus, I want to reduce the file size without compromising much of the quality. Here is the solution.
Using ffmpeg to reduce movie file size:
ffmpeg -i GrapheneAlNP-3kms-full.mov -c:v libx264 -r 30 -pix_fmt yuv420p out.mp4
The original movie file was created using old QTime (v.6 or 7?) using image sequence thus uncompressed. Seems that solution 1 fix the file size pretty well (3-7x reduction factor) with almost the same video quality. Nice!
Using ffmpeg to create movie from image sequence:
ffmpeg -framerate 24 -i FS5B-%06d.png -c:v libx264 -r 30 -pix_fmt yuv420p out.mp4
I found some old image sequence from my PhD year (Shift/collapse schematic with 3-4-5-bodies). Recreated the movie file using command above. The new movie file is 15x compressed! (150 MB -> 10 MB). Should have done it long time ago!
As a result, ~5 GB save!