* How video over IP works
We’ve used many newsletters to describe how VoIP works; this week, we’d like to review some basics on how video over IP works. As with voice, for video to be put into an IP packet it first must be converted into digital format and, as is also the case with voice, digital video is then compressed to maximize both bandwidth efficiency and to ensure quality presentation. Like voice, video is encoded at the origination point for transmission and then decoded at the end terminal.
Video encoding and session control is more complex than techniques used for voice because it must allow for a wider allowance of bandwidth, it must include protocols for presenting pictures on a multiple kinds of screens, and it must also include an audio component to allow for sound that accompanies the picture.
In the voice world, the ITU-T has established a series of standards including G.711, G.721, G.722, G.726, G.727, G.728, and G.729. And once digitized and encoded, voice transmissions (or sessions) are typically controlled by H.323 or Session Initiation Protocol, with SIP being the strategically controlled protocol.
For video, the two most common compression techniques—MPEG-2 and MPEG-4 were established the Motion Picture Experts Group. We should note that MPEG compression techniques can also be used for video that is sent over non-IP networks like broadcast cable television systems.
MPEG-4 Part 10 has also been incorporated into the latest ITU standards and this most recent standard is referred to as H.264 or Advanced Video Coding. MPEG-4 provides a significant improvement in both picture quality and it doubles bandwidth efficiency when compared to MPEG-2, MPEG-4 Part 2, or H.263 techniques. (For readers who’d like to see a visual display from a movie clip using the two different techniques, first turn down the volume on your speakers then click here.)
Once encoded, the video is ready for transmission onto a network. We’ll review different transmission media used for video next time.
