Ive just noticed something on Pond 5 when I search for my own videos. In many of my clips that have blue skies, I'm seeing heavy pixelation in the previews (when I hover the cursor over the video.) The blue sky is transformed into a series of blocks more or less. Same for underwater footage. Though when I click on the video and let it play within it's own page, it looks sort of decent. I first started noticing this issue with my GoPro videos and thought it was exclusive to them. I then searched for clips shot with my Panasonic G6 (which takes better quality video than the GoPro) and was surprised to see the same issue with them. Though oddly, other contributors' videos in search results look fine (even ones with blue skies.)

Just trying to work out why I'm getting this heavy pixelation with my clips on the Pond 5 previews. The same versions of the clips look fine on my monitor when they're played from my harddrive (prior to uploading them.) I admit I am using the h264 codec but I wouldn't think it would produce that extreme of a problem.

The bitrates of my cameras are not super high but when I export a h264 video from them for stock, I try and get the bitrate as close as possible to the original.

Perhaps you push the contrast limits in post? GoPros don't really have space for grading even if you shoot with their "flat" profile. Applying luts or high values in post drive output to this kind of problems.

I did no grading on the GoPro clips at all. I left them completely untouched. And with the Panasonic G6 time lapse clips, I only applied color grading to the Raw photo files and did none when I converted them to video format. But those Panasonic clips have the same problem in the previews.

Instead of the sky check the dark areas of your clips. Are they black solid or pixelated black?

Ive just checked two of the GoPro clips and the blacks look quite decent. Fairly solid blacks (including shadow areas.) But areas of blue are an absolute mess.

I think Pond5 is really compressing it's previews. I've noticed that many of the previews on my videos look really bad.

they have a reason for it.

Perhaps not, it is the low bitrate of our cameras that do not provide enough info, this way lower resolution clips might expose some artifacts