Search on these platforms with keywords. Gives both whole titles and segments of videos. Examples from Films on Demand:
Permaculture, Eco-forests Developing Green Economies: ... (26:59)
Sepp Holzer's Permaculture: Farming with Nature (28:59)
Starting a Produce Farm: The StartUp Experience (01:10:11)
Treating Earth like Dirt: David Montgomery (56:57)
From Kanopy - they collect videos under subject areas together: I searched "agriculture".
Use the Five Colleges catalog to find DVDs in our collection
(Titles from Films on Demand and Kanopy are also listed there.)
Link goes to catalog record
Fresh - New Thinking About What We're Eating 
Celebrates the farmers, thinkers and business people across America who are re-inventing our food system. Forging healthier, sustainable alternatives, they offer a practical vision for a future of our food and our planet. Among others, Fresh features urban farmer and activist Will Allen, sustainable farmer and entrepreneur Joel Salatin, and supermarket owner David Ball.
The Future of Food 
Documents the trend of unlabeled genetically-modified foods which have become increasingly prevalent in grocery stores. Unravels the complex web of market and political forces that are changing the nature of what we eat. Explores organic and sustainable agriculture as alternatives to large-scale industrial agriculture. There are also shorts on CSAs, farmer's markets, and other relevant topics.
Sonatas of the Soil, 2012
Several short films:
A Talk by Satish Kumar, 2008, 44 minutes
Transition Town Totnes 2008, 13:29 minutes
Portrait of a winemaker; John Fry of Frog's Leap, 2011,15 minutes
Sekem Vision, 2011, 14:03 minutes
Soil In Good Heart, 2008, 13 minutes
Walking and Talking with Vandana Shiva 2008, 54:16 minutes.
YouTube and Vimeo are two video platforms on the Web.