I have made a few videos with flights over the ocean, and in all cases the result is very poor. The video is 4k, color graded etc. The playback is fine inside Premiere, but after export that water kind of seems to jump about. Please see videos as examples:
That looks to be macroblocking, a common issue with highly compressed media especially visible on large areas of similar texture/color.
The compression is built by blocks of pixels ... 4, 9, whatever ... and looks for similarities. If it decides they're close enough, it makes them the same to save data space. So a block of 27/23/31: 26/24/31:28/23/30/26/22/29 might all become 27/23/31.
It's a problem with a lot of drone footage ... passes over like-covered foliage or grasses, ocean/lake/river water scenes, skies. Well, with skies for a lot of cameras.
Bumping up the bitrate or switching codecs can help. I know some who do all their YouTube uploads at decent levels of ProRes or DNx variants in the hopes of getting enough detail through the re-compression steps by YouTube to get around this.
is your final goal facebook video uploads? because you can click the gear icon and manually change the quality of the stream to HD or 2K.
when i selected 2K, it looked fine to me. I think facebook just has a really aggressive auto bandwidth selector.
but if you want to squeeze a couple more jiggawatts of quality into the video, try a low cineform 10 bit. it will encode as a wavelet instead of a dct macroblock and import as 4:2:2 color so you may get 10% better upload quality.