I remember this, there actually was a problem with the video Null had posted that made it not play in browsers. I don't supposed he ever apologized for being wrong, either.
In particular, I believe it was because he was using yuv444p color encoding, which is a very detailed color encoding. Most mp4 videos are yuv420p, due to it being far more compressible, and as a result a lot of mp4 players don't support yuv444p (I don't have a ton of knowledge on the subject, so I can't really explain why any of this is the case). A quirk of yuv420p though is that it only works on even pixel dimensions. As a result it is impossible to encode a video with an odd aspect ratio using yuv420p, atleast without just cutting off or adding a line of pixels (which is what I did).
Now as for why josh chose to use yuv444p, its possible that whatever program he used to make it decided that since he was using a png image source yuv444p was the better choice (basically prioritizing quality over compatibility), or whatever program he was using used yuv444p as a last resort because his input was an odd aspect ratio. I didn't know any of this the time, all I knew was "video doesn't play on browser or media player but can be played with ffplay" and I just tried to recode it using "max compatibility" settings for ffmpeg that I found on the internet. Then I ended up resizing it so those settings would actually work, because yuv420p could not encode the video.
And no, he never apologized or retracted anything lol. Not that I care about that, its more the fact that he knew what browser I was using and felt the need to share it.
Its a pretty dumb thing to assume if he didn't "somehow" know. A lot of tards still use outdated browsers or mobile browsers or apple's mobile browser, and all of those are more likely to run into issues with a video file you hacked together without knowing what you were doing than firefox.
