Glossary

Multi Bitrate

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multi bitrateMulti bitrate streaming is devised so a viewer can have better access to videos by synching the video’s resolution and bit rate with the viewer’s optimum connection speed. It works by encoding a video at different bit rates to accommodate varying bandwidth connections resulting in faster video streaming without the buffering.

The player used to view the video will evaluate the bitrate of the video compared to the available download bitrate. If there is more bandwidth available, then the player will request the next highest bitrate of the video. The player analyses the two variables (available download speeds/bitrate and the bitrates of the downloaded video) over set periods of time, usually 2 to 10 seconds. Each time period the bitrate of the video played will be optimised to the network conditions at that time.

This may mean that the video quality may vary greatly if the connection between the viewer and the network changes often. This might happen when someone is streaming a movie while traveling in a car into areas of good mobile network coverage and then not so good coverage. Even ethernet or wifi networks can fluctuate over the course of a day so the streaming quality of a video may differ based on local usage of the network.

Multi bitrate is also referred to as adaptive bitrate streaming. Its technology is based on HTTP with support for large networks like the Internet. Its origins date back to 2002 and a working group in the DVD Forum. Today there are several implementations of multi bitrate technology including MPEG-DASH, Apple HTTP Adaptive Streaming, Adobe Dynamic Streaming for Flash, and Microsoft Smooth Streaming.

While it takes more effort upfront to encode the video into the various bitrates the end result for the viewer is much better. Someone trying to stream a high bitrate video under poor network conditions will become frustrated at the buffering, possibly audio and video getting out of sync, artifacting, or failure to play the video at all.

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