728×90 Leaderboard — filled by companion ad during ad break (if any), static image otherwise
300×250 Medium Rectangle
300×600 Half Page — static house ad (not a companion slot)
Static fallback images occupy all ad zones when no programmatic ad is active. During an ad break the companion slots (leaderboard and medium rectangle) are automatically replaced by the ad creative delivered alongside the audio/video ad. After the break the orignal images are restored.