>>94339
Decoded format: Planar 4:2:0 YUV 10-bit LE
tells you it was 4:2:0 chroma subsampling (good) but 10-bit bit depth
for browser playback you want 8-bit
in ffmpeg terms, you want to specify -vf format=yuv420p (or the shorthand -pix_fmt yuv420p)
your encode defaulted to yuv420p10le because your source was 10-bit, presumably