Experienced the same problem this morning.
As for channel
, it is using the H.264 codec, "
At some point last decade, H.264 was made an optional part of ATSC 1.0 that almost nobody has implemented, though Mexico permits it." - T.E. Some 4K TVs can pick up the Video (test pattern) and audio tones; not intended for public consumption.
H.2645 will be the codec used in ATSC 3.0.