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Adaptive bitrate streaming
Adaptive bitrate streaming is a technique used in streaming multimedia over computer networks. While in the past most video streaming technologies utilized streaming protocols such as RTP with RTSP, today's adaptive streaming technologies are almost exclusively based on HTTP and designed to work efficiently over large distributed HTTP networks such as the Internet.
It works by detecting a user's bandwidth and CPU capacity in real time and adjusting the quality of a video stream accordingly. It requires the use of an encoder which can encode a single source video at multiple bit rates. The player client〔(DASH at ITEC, VLC Plugin, DASHEncoder and Dataset ) by C. Mueller, S. Lederer, C. Timmerer〕 switches between streaming the different encodings depending on available resources.〔(C. Müller, S. Lederer and C. Timmerer, “An Evaluation of Dynamic Adaptive Streaming over HTTP in Vehicular Environments”, In Proceedings of the ACM Multimedia Systems Conference 2012 and the 4th ACM Workshop on Mobile Video, Chapel Hill, North Carolina, February 24, 2012. )〕 "The result: very little buffering, fast start time and a good experience for both high-end and low-end connections."
More specifically, and as the implementations in use today are, adaptive bitrate streaming is a method of video streaming over HTTP where the source content is encoded at multiple bit rates, then each of the different bit rate streams are segmented into small multi-second parts.〔(S. Lederer, C. Mueller and C. Timmerer, “Dynamic Adaptive Streaming over HTTP Dataset”, In Proceedings of the ACM Multimedia Systems Conference 2012, Chapel Hill, North Carolina, February 22-24, 2012. )〕 The streaming client is made aware of the available streams at differing bit rates, and segments of the streams by a manifest file. When starting, the client requests the segments from the lowest bit rate stream. If the client finds the download speed is greater than the bit rate of the segment downloaded, then it will request the next higher bit rate segments. Later, if the client finds the download speed for a segment is lower than the bit rate for the segment, and therefore the network throughput has deteriorated, then it will request a lower bit rate segment. The segment size can vary depending on the particular implementation, but they are typically between two (2) and ten (10) seconds.〔〔
==Current uses==
Post-production houses, content delivery networks and studios use adaptive bit rate technology in order to provide consumers with higher quality video using less manpower and fewer resources. The creation of multiple video outputs, particularly for adaptive bit rate streaming, adds great value to consumers. If the technology is working as designed, the end user or consumer should be completely unaware of it. Therefore, even though media companies have been actively using adaptive bit rate technology for many years now and it has essentially become a standard practice for high-end streaming providers, mainstream consumers are relatively ignorant of its necessity.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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