Be careful what you wish for.
You can''t sex Bettas when they are small and, depending on what type(s) you breed, you may not be able to tell sex until they are old enough to start blowing nests ( This is mainly the Plakat Bettas). What the pro breeders do is separate the males into 1 gallon containers when they start showing elongated fins (if they are showing them in competitions) or when they start fighting. Usually, spawns that are raised together will usually not fight for a longer period of time so you could wind up with a number of fully developed males that aren't fighting. HOWEVER, once you separate them, the odds of successfully putting them back together with a good outcome goes way down. There is also a downside to raising the spawn for long periods of time together. The more dominant fish of the spawn will release a hormone preventing their siblings from developing so you can wind up with a number of runt fish that won't mature until you remove the other fish and the hormone from the water ( through water changes).
The breeding process is more than just watching for the eggs to drop. I'm not sure what video you saw this on but there needs to be direct contact between the male and female or the eggs don't get fertilized so unless this video showed that, those eggs were not going to hatch. I have had females get so excited while waiting for their males to build a nest that they released their eggs in the jar ( I introduce my females first through visual contact in a separate jar) but again, those eggs will be duds.
Another thing you may not be aware of with breeding bettas is that it can be a brutal experience and tough to watch. Many females are killed in the breeding process. Both fish in the pair can have their fins shredded and they may not always grow back to what they were when they started. I always suggest that if you like your betta the way it is now, DON'T breed them.
Get others for breeding purposes.
Now, having said all that..... I strongly suggest you read this article (all 4 parts) before you decide what you are doing.
breeding bettas
Hope this helps