AV1 and VP9 are covered by plenty of patents. One of the differences here is that there is a retaliation clause in the licenses for AV1 and VP9. https://aomedia

AV1 and VP9 are covered by plenty of patents. One of the differences here is that there is a retaliation clause in the licenses for AV1 and VP9. https://aomedia.org/license/patent-license/ https://aomedia.org/license/patent-license/ "1.3. Defensive Termination. If any Licensee, its Affiliates, or its agents initiates patent litigation or files, maintains, or voluntarily participates in a lawsuit against another entity or any person asserting that any Implementation infringes Necessary Claims, any patent licenses granted under this License directly to the Licensee are immediately terminated as of the date of the initiation of action unless 1) that suit was in response to a corresponding suit regarding an Implementation first brought against an initiating entity, or 2) that suit was brought to enforce the terms of this License (including intervention in a third-party action by a Licensee)." This makes it much harder for practicing entities or their licensees to assert claims against other practicing entities over the formats.