Ask HN: Did the White house edit Trump coughing out of this video?

This is technical rather than political question: https://twitter.com/realDonaldTrump/status/1312525833505058816 is the video - the question is after 1:01 when he says "the therapeutics, which I'm taking right now [facial movement, cough?]?

I thought no, but if you watch the US flag on the left the pattern suddenly jumps from frame to frame (ignoring the motion of his face, which is unnatural, but he is ill)

Compression artefact or what? I'm not knowledgeable in neither video editing nor compression algorithms.