i have not had time to do the openads guide yet but i'll put you on the right track.

in your view_video.tpl put your banner code in with the source as "{insert name=video_keyword assign=keyword vid=$VID}{section name=j loop=$keyword}"

if you wanted the channel put "{insert name=video_channel assign=channel vid=$VID}{section name=k loop=$channel}" in instead

When the user views a video it will then display the banner code with the video or channel (or both if you want) keywords as the banner source keywords.

etc

hope that makes sense....i have not intergrated openads into my site just yet as i have been too busy, but from my quick inital tests it looks like it would work fine, i hope to have a more detailed guide up when i get round to adding it to my site, which should be soon.