So, I set about trying to find a setting that would work for a 1024×768 screencast. The majority of settings produced some weird-quality results, even with the quality settings turned up as high as possible, which makes me think it had something to do with a faulty interlacing/deinterlacing setting somewhere. When I changed the one interlacing setting I was able to find, the exported videos would work fine in QuickTime, but look completely messed up in VLC and, more importantly, YouTube.

Exporting to F4V actually did work in every media player I tried it in, but for some reason, YouTube was unable to convert it to a playable format.

Finally, after about 9 hours of fiddling with Adobe Premiere Pro’s Export Media dialog, I found a setting of acceptable quality that worked on YouTube. I doubt many other people will need this, but since I was unable to find any information about the problem I was having online, maybe I’ll save another person 9 hours of work. Here are the settings I used:

Export Settings
Format: QuickTime

Filters
No Changes

Video
Video Codec: H.264
Quality: 100
Width: 1,024
Height: 768
(Width and Height are unlinked)
Frame Rate: 30
Field Type: Lower First (this was the setting that deals with interlacing I believe)
Aspect: Square Pixels (1.0)
Render at Maximum Depth: Checked
Set Key Frame Distance: Unchecked
Optimize Stills: Checked
Frame Reordering: Unchecked
Set Bitrate: Unchecked

Audio
No Changes

Others
No Changes

I’m sure there are some optimizations to be made in these settings; things that are causing me to produce unnecessarily large files, things that make rendering slower, or things that, if I tweaked, would give me even better quality. However, after 9 hours, I don’t care; this works, so for now, I’m done. Hope this helps someone.