The camera angle on the video shifted. It zoomed in on the 'Elias' in the video. The zoom was impossibly smooth, digital enhancement on a level that didn't exist. It zoomed in on the terrified man's eyes.
If you have a library of thousands of MP4 files, you don't need to re-encode everything. However, you should consider your most critical files. The update is backward-compatible at the container level, but to get the new speed features, the file must be rewritten with the new structural boxes. mp4 mania upd