why frameformat instead of pixelformat?

Hello,

while reading into the media-api issue I found out that for configuring the entity pads a frameformat is used.

For that I found the negotiation rfc of that topic, but I don't really get the relevance of a frameformat.

http://www.spinics.net/lists/linux-media/msg10006.html

Can anyone explain why the media-api uses the frameformat instead of the pixelformat and what the main differences are?

Thanks in advance.

Best regards,
Tom