how to convert my own video to hdf5

i tried to convert my own video to hdf5.but i think it's not the same structure as the box.h5.the box.h5 has 3 keys: box, ell and framesIdx. box is the frame, framesIdx is the number of frame, but i wonder what the ell is.
By the way, must i use the hdf5, can i just use the videos?if i must use hdf5, how to convert my videos to the hdf5 which is similar as your hdf5 file? 