That's not anticompetitive though, it's purely competitive. Amazon has better underlying economics (because it has deployed capital to build infrastructure) and therefore is able to offer the same service at a lower price.
It's very hard to imagine a situation in which Amazon could lock new entrants out of the video encoding market. All you need to enter this market are a fast connection and a server farm, both of which you can get for yourself or rent from numerous IaaS providers.
Amazon might very well have a price advantage, but other parties that can offer better quality of service or better L10n or whatever will still attract customers. This is how markets are "supposed" to work.