基于CMAF的直播平台搭建笔记1--DASH播放器,OBS推流

CAMF的演变

CAMF是基于HTTP1.1的分段编码传输方式实现基于chunk的超低时延传输
在CMAF之前已经有相关研究论文
2011年:有学者研究如何通过分段编码实现超低时延传输
2013年:有学者提出可以通过HTTP1.1协议实现分段编码的超低时延和开销传输,但是没有标准化和真实的应用.
2015年: 微软和苹果共同开发,CMAF白皮书出现,将DASH和HLS整合到一起
2018年:国外的许多流媒体公司已经实现CMAF框架的商用,但是国内仍然是起步阶段.

CMAF框架下需要解决的问题

1. 在CMAF框架下,ABR码率自适应算法的研究问题: Review of the ABR switching logic, which may need some optimizations (or a new mode) when dealing with very small forward buffers. Additionally, the safety ratio of estimated throughput over bitrate-we-are-willing-to-play should be raised in this mode to protect against fluctuations in throughput draining the small buffer.
2. HTTP chunk 和CMAF chunk是否对齐(whether each http chunk is always aligned with each cmaf chunk.) That is, do those have same size? If not, could the end of a http chunk be in the middle of a cmaf chunk by some kinds of proxy servers? https://akamaibroadcasteruseast.akamaized.net/cmaf/live/657078/akasource/out.mpd

DASH平台下,CMAF框架的演进

1. 2017年 11月 Edgeware already have a branch development with some of these changes. A player from this branch is available here: https://vm2.dashif.org/chunked-player/samples/dash-if-reference-player/ (Chrome only). It can play 8s segments (1s chunks) with only 4s end-to-end latency. Since the buffer is ~3.5s, it should be possible to wring another 3s of latency out of that implementation (if the implementor wants to live with a 0.5s forward buffer.) 其已经实现了端到端的延迟与segment的长度无关,取决与客户端的缓冲区大小.