Detailed analysis of the footage is not necessary. The whole world could see that he was writing on something on the podium during the debate. What was he writing on? Something that was not there before he took the stage and something that did not belong there.
Section 5, pages 4-5 of the binding "Memorandum of Understanding" that was negotiated and agreed upon by both political campaigns states:
"No props, notes, charts, diagrams, or other writings or other tangible things may be brought into the debate by either candidate.... Each candidate must submit to the staff of the Commission prior to the debate all such paper and any pens or pencils with which a candidate may wish to take notes during the debate, and the staff or commission will place such paper, pens and pencils on the podium..."