If you ever use the Facebook app on your iPhone in order to take video and post to your timeline, you may have noticed that by default the quality is diminished. While Facebook does a fair amount of compressing on their own to save bandwidth on their end, you can tell Facebook to always record video in HD, resulting in higher quality videos.
Before following the steps below, be aware that this only works if you have the native iPhone or iPad app installed. This will not work on the mobile web version.
That's it. The native Facebook app will now default to HD video resulting in what should be higher quality uploads. This will however come at the cost of longer wait times to upload videos since the files will be larger in general.