Thanks so much guys for the responses. Here is more info. I got all of the clips, mostly videos on the brain, from Youtube, by using keepvid.com. On that site, it lets you "save link as" for many sizes. I usually chose 480p or 780p. It occurs to me if it expanded the smaller ones that could degrade quality. I don't really know what "codec" means, I am a total beginner, but can say what I did.
Following the tutotial at
https://helpx.adobe.com/premiere-pro/how-to/export-sequence-clip-premiere-c... I did:
export media
entire sequence
format H.264
preset HD 1080p 29.97 (this may have caused blowing up 480p and 780p to 1080p which would cause quality
issues too, maybe)
Variable bit rate with 2 passes
bit rate to 256
choose output name,location
After writing this, I am wondering if my main problem is expansion of the size of the original clips. That's one reason I wanted to export the sequence uncompressed thinking that would prevent size changes but it seems that is not true. Maybe I should be asking in addition to what format to export in, how to make sure it does not change the pixel size of the images?
Thanks
Jim