MP4 Output and Preloading Improvements

This update provides an optimized playback experience for short-form videos under two minutes in length by providing MP4 renditions. We have also improved our preloading logic and updated recommendations for building performant video experiences with the Livepeer Player in React or React Native.
By enabling streamlined file downloads and simpler preloading, this update drastically improves time-to-first-frame (TTFF) for short videos. Our internal tests have demonstrated sub-second TTFF for non-cached video and near-instant TTFF for videos that have been cached by the CDN.
If you are using Livepeer.js, please upgrade to @livepeer/react@2.2.3
 or @livepeer/react-native@1.2.3
.
Specific changes:
We will now generate MP4 renditions for VOD uploads under two minutes in length, in addition to HLS renditions.
The Livepeer React and React Native players have been updated to prefer MP4 renditions when available. If you are using your own player, we recommend that you implement logic to do the same. 
We've added a new usePlayerList hook to the React Native player to make it simpler to use the player in a list
When retrieving playback info, the Livepeer API response will include MP4 renditions in the source array when available
We’ve created an example application to demonstrate how you can use dynamic preloading to create a performant short-form video experience.