Pictures are now drag n drop I haven't hit a size limit with the new forum change over. Videos are better linked from you tube or airvus type hosting sites.
You can do that two ways now. you can post a link using the url and the chainilink icon at the top of the chat window. Other wise as I do is open the icon with the three dots and the down arrow for inserting things and drop the page addy in the media part of the pull down so it shows in the post.
This is how links show. (hrrmmm last time it did this it did drop a link not show the video)