OMXplayer doesn't appear to support yuv444p videos

[pgbconfirmit]

Is it feasible to add support for yuv444p?

[popcornmix]

No not supported by the hardware. Depending on resolution you may be able to play them with VLC or kodi (which can software decode).

[walterav1984]

You may try mjpeg codec with 422 instead of 444.