That is definitely the High Frequency Global Communications System (HFGCS). You can see later in the video that the receiver was tuned to 4724.0 kHz USB.
Primary HFGCS voice frequencies are 4724.0 kHz, 8992.0 kHz, 11175.0 kHz and 15016.0 kHz. EAMs are generally transmitted in simulcast, I.E. all 4 of the frequencies simultaneously. A daily change of call sign will also generally occur. For example, the March 29th call sign was RIDERLESS and the April 2nd call sign was PRESCOTT.
Typical message format:
02 APRIL 2021 11176.0 kHz USB (simulcast)
21:46Z
FM: PRESCOTT
ALL STATIONS ALL STATIONS, THIS IS PRESCOTT, PRESCOTT, STANDBY MESSAGE FOLLOWS
7YYVJE // GW4VA VFX44 EYY4V EOYKV JGIN
22:00Z
FM: PRESCOTT
7YYVJE // GW4VA VFX44 EYY4V EOYKV JGIN
THIS IS PRESCOTT, STANDBY, MORE TO FOLLOW
22:03Z
ALL STATIONS, ALL STATIONS THIS IS PRESCOTT, PRESCOTT BREAK
7YMYCA // TZGSC NJLEV UVOYJ RF4IR EMF6
22:05Z
ALL STATIONS, ALL STATIONS THIS IS PRESCOTT, PRESCOTT BREAK
7YEXVN // Y6JAF OZJIL FC45H II5RF GVAJ
22:08Z
ALL STATIONS, ALL STATIONS THIS IS PRESCOTT, PRESCOTT BREAK
7YEEGL // 45ZXY FNVJW IBQWU IJARY I3ED
22:10Z
ALL STATIONS, ALL STATIONS THIS IS PRESCOTT, PRESCOTT BREAK
7YZWYL // Y25RB ZD7YQ DNJKT 6KFFE RGA3
And I just so happened to have caught one while I was writing this post.
08 APRIL 2021 11176.0 kHz USB (simulcast)
00:00Z
FM: MADELINE
7Y6WGY // 2LG6S I2AXH ETEKT OOILH SWDY
RSPduo | Barker & Williamson, end-fed longwire and Wellbrook loop antennae | Toronto, Ontario Canada