Lay the ribs on the top rack of the grill (away from the coals, if you're using briquettes). Reduce gas heat to low, close lid, and leave undisturbed for 1 hour. Do not lift the lid at all. Brush ribs with barbecue sauce, and grill an additional 5 minutes.
You can store about 27 hours and 30 minutes of video on a 64gb memory card.
The most accurate way I suggest for you to work this out is to create a small amount of video (say, 1 or 2 minutes) of the type you plan to put on your SD card, see how big the resulting file is, then extrapolate from there to work out how many minutes 1 Gb will hold.