I have no answer for the measurement. As most of us know, it's irrelevant and who pays attention to something that's irrelevant? Just add the additional time to your bill. Tell the client why it took longer, and why you had to do it -- to unnecessarily placate Mr. Clueless.
I once worked with a designer who could never wrap his head around 29.97 frames per second. "How can you render just part of a frame?". I don't think the guy has gotten it after ten years.
There are no inches in the video for web graphics for that matter. Never have been.
After Effects should not put any metadata at all on the PNG sequence that has anything to do with pixels per inch. Mine come out at 72 when imported into Photoshop.
yep it's weird - sometimes I get 72 ppi as well, and sometimes 2.54 ppi.
is there a way to simply change metadata without needing to open in Photoshop to change?
Unless you are printing the image sequences the PPI is meaningless. Resolution is number of pixels, print size is controlled by the ppi. PPI makes no difference on the web or in video.
Download these bad boys and check them out in Photoshop and Word or Pages or anything related to bring. You'll be lucky if you can find the 9999PPI