Here in Chicago, WCHU, channel 3 (RF7) has been messing around with their subchannels lately. On my TV and in a Chicago OTA forum, it was noted that they had made more changes this week.
I did a rescan but it only found 3-1, -4 and -5. I didn’t bother to save the new scan. As a test, I added -1 through -7 to my guide. This is what was found on the last scan a few weeks ago. All worked except -2, which said “Weak Signal”.
This was curious, and on that OTA forum, asked if anyone could tell if they are using AVC/MPEG4. According to one user, they are on -2, -3 and -6 through -9.
I have a Legacy Tablo HDMI, and it seems it may actually support MPEG4 broadcasts if the channel scan would allow it.