Edit: NOTE, I am the receiver of the texts.
So many people asking me to have my wife do something different on her end.
Beloved, she is on iPhone because she doesn't want to do anything "weird." She is texting from her phone number using her texting app. That's what's going to happen.
Now, why can't I get iMessage on my android phone? If it's just a messenger app why not make it available for Android?
I'd use it.
Its due to compression of the video in order to fit on a MMS message, which is very small. Android uses RCS as a new message standard that can send bigger files but Apple has yet to add it to their OS. Its similar to how Apple uses iMessage to do the same, however this is not a standard and is locked to only apple devices.
Apple is supposedly adding support for RCS during the new iOS update but until then you can use a different messaging app to send better/larger files.
I recommend Signal as it is easy to sign up and start using while also being private.