"What is the best action stock footage for effects such as explosions, fire, smoke, etc?"
Since the term best is so subjective, this is really asking 2 distinct questions:
In this video I will answer both of those questions!
All of the elements are perfectly exposed, come in resolutions up to 4K and are often shot in slow motion. For rendered elements such as the ground cracks and ground burst effects, you also get separated render passes for shadow and Z depth. Their products are not cheap, but you can decide to purchase entire collections or individual elements depending on your budget and your requirements. Single elements range from $15 to $30 and full collections from $199 to $499.
If you run a movie studio and have access to a larger budget, you may want to consider purchasing the ActionVFX drive. The drive includes all of the ActionVFX collections, 1316 individual elements in full 4K and they will ship it to you on a physical drive to save you hours or days of downloading their media online.
The pack is pretty reasonably priced at $99.95 for the 720p version and $249.95 for the 2K edition. The reason this pack is so popular and I would recommend it if you are just getting into film making and visual effects is that it includes over 500 stock footage elements across 20 different categories so you get a very large variety of effects to work with. It includes fire, smoke, explosions, dust, debris, impacts, dirt hits, bullet shells and much much more. It even includes some bonus content such as grunge textures and a handful of sound effects.
If you are looking for something affordable to get you started, this is the pack I'd recommend.
The Explosion Assets pack contains 12 unique explosions, rendered from 4 angles each so you end up with 48 individual assets. There are a few debris assets included as well and the pack will set you back $99.99.
The Fire Assets come with 30 unique fires, plus additional versions for ignition and looping, giving you a total of 45 fire stock footage elements. This pack is a fair bit cheaper than the Explosion Assets at only $29.99
All of the elements from these packs look like they have been generated and rendered out in SideFX Houdini and they look nice and detailed. I especially like that the explosion assets look nice and dirty and with some colour correction and colour grading you can easily blend them into your own footage.
If you intend to get both the Explosion and the Fire Assets pack, you may consider just snatching the Pyro Bundle at a slight discount, costing $119.
So now that we talked about the best quality action stock footage, let's check out what the best free options are!
All of their stock footage elements are free to use, just make sure you include a link back to their channel and give them the appropriate credit!
The Detonation Films website isn't that great to navigate but they contain some great free action stock footage if you know where to look. Here are the links to their free elements:
In order to download the free elements, scroll down to the bottom of each page and click on the big Detonation Films logo.
A form will pop up asking for payment. If you like what they do, please consider giving them a little bit for their effort, but you can just as easily specify the price as $0 and proceed through the checkout process. You will have to provide your email address and you will be emailed a link to the free stock footage download.
Footage Crate's website has seen a fairly recent face lift and now offers a pretty big range of both free and paid stock footage elements across a very large number of categories.
You can find plenty of free elements elements that you can download and use for free in your own film projects.