Looking at the source of your comment, that’s WEBM in MP4 clothing.
ETA Media Info:
General Complete name : img_E009A241FEE37525183350662ED905D0E523DA78D6F777D498512F880D968DCF.mp4 Format : WebM Format version : Version 2 File size : 80.6 KiB Duration : 1 s 500 ms Overall bit rate : 440 kb/s Frame rate : 10.000 FPS Writing application : Lavf60.16.100 Writing library : Lavf60.16.100 FileExtension_Invalid : webm Conformance warnings : Yes General compliance : File name extension is not expected for this file format (actual mp4, expected webm)
Video ID : 1 Format : VP9 Format profile : 0 Codec ID : V_VP9 Duration : 1 s 500 ms Bit rate : 416 kb/s Width : 444 pixels Height : 222 pixels Display aspect ratio : 2.000 Frame rate mode : Constant Frame rate : 10.000 FPS Chroma subsampling : 4:2:0 Bit depth : 8 bits Bits/(Pixel*Frame) : 0.422 Stream size : 76.2 KiB (94%) Writing library : Lavc60.31.102 libvpx-vp9 Default : Yes Forced : No Color range : Limited