MPEG-DASH基本介绍

Dynamic Adaptive Streaming over HTTP (DASH), also known as MPEG-DASH, is an adaptive bitrate streaming technique that enables high quality streaming of media content over the Internet delivered from conventional HTTP web servers.

MPEG-DASH是一种码流自适应的技术，它可以在网络上(利用HTTP web servers)传输高质量的媒体流。

Similar to Apple's HTTP Live Streaming (HLS) solution, MPEG-DASH works by breaking the content into a sequence of small HTTP-based file segments, each segment containing a short interval of playback time of content that is potentially many hours in duration, such as a movie or the live broadcast of a sports event.

和HLS类似，MPEG-DASH将内容分割成一系列很小的文件segment，这些segment可以通过http直接访问。每个segment包含一小段时间长度的内容。

The content is made available at a variety of different bit rates, i.e., alternative segments encoded at different bit rates covering aligned short intervals of playback time.

存在多种不同码流的content， segment也被编码成不同的码率， 并按照时间对齐。

While the content is being played back by an MPEG-DASH client, the client automatically selects from the alternatives the next segment to download and play based on current network conditions.
The client automatically selects the segment with the highest bit rate possible that can be downloaded in time for playback without causing stalls or re-buffering events in the playback.
Thus, an MPEG-DASH client can seamlessly adapt to changing network conditions and provide high quality playback with fewer stalls or re-buffering events.

当MPEG-DASH客户端播放content时，客户端可以根据当前的网络情况，自动下载合适的下个segment。
客户端可自动选择目前状况下，最适合播放的高码率segment来播放。因此，MPEG-DASH客户端可实现适应网络状况变化。

A media presentation description (MPD) describes segment information (timing, URL, media characteristics like video resolution and bit rates), and can be organized in different ways such as SegmentList, SegmentTemplate, SegmentBase and SegmentTimeline, depending on the use case.

mdp用于描述segment的信息，比如时间、url、视频的分辨率、码率等。

Segments can contain any media data, however the specification provides specific guidance and formats for use with two types of containers: ISO base media file format (e.g. MP4 file format) or MPEG-2 Transport Stream.

Segments可以包含任何媒体数据，关于容器，官方提供了两种建议: ISO base media file format(比如MP4文件格式)和MPEG-2 Transport Stream。

References:

https://en.wikipedia.org/wiki/Dynamic_Adaptive_Streaming_over_HTTP