Why are the videos I receive from other Iphone users varied in size and clarity?

That would also have an impact. If you were just using MMS, which is the media function of SMS, which is a carrier function, those videos are always compressed for space, and always sent at a lower resolution.

You cannot downgrade iOS. Apple does not provide a path to do that. As far as the quality of the videos you receive, that is determined by the sender, not you. If this seems to always come from the same sender, have them check their settings for taking video, and then sending it. If set for compression, it will have a definite effect on what you receive.

While there are settings in Camera for video quality, the balance are in Messages. In Camera, they can check and set the resolution for recording video there. When it comes to what is sent, that is done in Messages. They would need to check the setting for Low Quality Image Mode. Turning that on sends a lower quality image. It can also matter at times if you are on cellular data versus wi-fi when sending.

BeeSandee wrote:

The videos are very small, almost thumbnail size...

Video content within Messages can play directly within Messages (maybe this is your thumbnail size issue) or they can play full screen (which may be better resolution).

It sounds like you're tapping the Play icon and playing directly within Messages -- maybe tap anywhere else in the video thumbnail to bring it full-screen, then tap Play.

iMessage is Apple's messaging service, and works with data, not the cellular channel as SMS does. Your decision to use it can be based on your data use. It was originally designed to reduce phone charges for SMS, that used to be charged by the message in the past. Send as SMS is another Apple setting, and that is for use when you are attempting to send an iMessage to someone and they may not be available to receive on, maybe not connected to data at the time, and the phone will then send it as an SMS if the switch is on. MMS Messaging is for text messaging that have media attached, such as a photo or video. That setting will also expose the switch for Group messaging, and it has to do with how they are put together.