It would be spectacularly difficult to do for videos: first there's lossy compression, which means that there's no guarantee your injected pixels survive the e

It would be spectacularly difficult to do for videos: first there's lossy compression, which means that there's no guarantee your injected pixels survive the encoding pass. Then there's the additional hurdle of motion vectors, which will most likely be misaligned between the original video and the injected one. This would result in hard to predict artefacts after encoding. Finally, each decoder handles scaling slightly differently, so even if your embedded video trick works on one software/hardware decoder, it might fail on another (sometimes even depending on just the version or additional settings/filters being enabled).