Live Video Streaming to Server

[Nicolas Dufresne]

Le jeudi 16 avril 2020 à 16:25 -0500, strange_loop a écrit :
> hls seems to be not supported in major browsers, however my problem is that

See https://github.com/video-dev/hls.js/ it's widely used for the
purpose. But indeed, HLS is not natively supported in browsers in
general as it's not part of the standard.

> what is the role of the server is this scenario.
> Like okey I used  pipeline and video.js but how does my stream reaches the
> client, over internet? How does it distirubuted?
> 
> I am trying to create a mental model, so that I will know what tool serves
> which purpose.
> 
> I am very new to streaming, I basically know very little about it.  

Streaming capabilities of browser is really poor in fact. That's mostly
because the browser offers very high level solution where normal OS
gives you low level UDP socket to play with.

In the case of HLS the flow is the following:

Server:
  - A server (your RPi) encode and mux into MPEG TS
  - It then split the MPEG TS in chunk and update a m3u8 playlist
  - Another server (e.g. nginx) picks these files from disk to make
them available to your browser

Browser:
  - The javascript will download though HTTP the m3u8 file and the MPEG
TS chunk
  - As MPEG TS is not supported by browser, it will transmux to
fragmented ISOMP4 (yes, in JavaScript!)
  - Is passes the chunk to the MSE JavaScript interface
  - That get decoded and played on screen (using a video tag)

If you use mpegsash, it's a bit lighter, since there is no transmuxing,
you need a JS library still. For video conferencing it's a bit complex,
but I'll keep it simple.

You need 2 peers, and web server. Potentially a STUN and/or TURN server
if the two peers have too restrictive network.

  1. Peers call each other through the web server
  2. They will use the web server to exchange some info: 
    - Network candidates, for ICE negotiation (nat traversal protocol)
    - SDP to negotiate the transport and encoding
  3. When a "connection" is established things goes peer-to-peer
    - A DTLS connection is established (server no longer see what is
going on)
    - RTP and RTCP packets starts flowing

Of course, when you go into big conference, the server becomes your
peer so that it can do video and audio mixing. In that case, the server
can see everything that is going on.

In the old days, there was some "video streaming" that was using image
tags and refreshing it. I think this is still possible using JPEG
compression.

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