Webinars , Unified Web conference plateform are designed for smaller groups, from meeting-sized groups to online events involving 5 to 25 of people. They often include many of the options available with online meetings, such as Q&A, polls, whiteboard and markup abilities. So webinars are full-featured presentations or events for a few 10-25 or (often) far fewer 2-5 individuals.
Webcasts : These are primarily with video and slides or video-only and are based on a video-to-user model. In other words, they’re more like a event show (possibly live) than a meeting. Large webcasts can handle hundreds or even of thousands of viewers. So webcasts are audiovisual experiences aimed at larger audiences, with the trade-off being fewer options for the end users.
Video streaming is the delivery of video and audio over the web. Video files are accessed via a link on a web page. on other side Playback is through an ordinary PC, laptop, computer or mobile phones without videotapes or DVDs etc..