So breathy voice involves both vocal fold vibration coming from the ligamental folds, and at the same time, continous leaking voiceless airflow through the arytenoids – hence the name ‘breathy’.
Now play the first movie. You should be able to see both the ligamental fold vibration, and also make out a dark space where the arytenoids remain slightly open.
Now play the movie of ‘breathy [i] slow’ to see how it looks with the help of a stroboscope.
Producing sounds with breathy voice is not a mechanism for contrast in English. However in some languages breathy voiced stops contrast with normal voiced stops. For example in Hindi (where these sounds are written as ‘bh’ and ‘b’ respectivelv), we find the minimal pair of contrasting words: