Do all TrueAlerts sound like this?

In this video, the truealerts have a rather weird code-3 pattern, in other words, some pulses are held for a longer duration while others are not. What is the reason for this.

That’s because they’re being coded by a SmartSync module. Its code 3 is a bit weird, like:
Beeeep-Beeeep-Beeeep Bee’eeeep-Beeeep-Beeeep.

As for the horn tone, SmartSync TrueAlert horns (4906, 4903-941X, 4901-9820) have a deeper, less shrill sound than conventional ones.

The panel looks to be a 4010 which has internal SmartSync capability on the NACs, so SmartSync modules are not needed. The strobes are synchronized by an 8ms to 15ms power drop to 0V every second. The strobe flashes on the momentary power drop. The horn timing is done internally in the devices. A digital code is sent to the devices to tell the horn how to sound or to turn off. This code is sent to the devices during a strobe sync pulse. To keep the horns in sync with each other the digital code is repeated periodically. That strange Bee’eeeep now and then is probably happening when the refresh comes from the panel.

The modules do it too sometimes.

The modules also refresh the horn timer in the SmartSync A/Vs, so the same odd beep can happen. The timer circuits that control the horn are subject to component tolerances. If not periodically refreshed the horns would eventually drift out of sync.

And the reason the horn and strobe have to be timed internally is so that both can be synchronized over the same pair of wires, correct?

Only the horn is timed internally in the A/V devices. The strobe synchronization is done using pulses to 0 volts done by the panel or sync modules. If using multiple sync modules there is a wire pair run between them so they all stay synchronized.

How is it possible that the horn sounds, if it is putting out 0V for the strobe to flash? TRUEALERTS ARE SO CONFUSING!!!

The strobe sync pulse is a maximum of 15 milliseconds, 0.015 second. A capacitor in the horn circuitry can cover that short time.