Overview

For optimal pucture picture quality with available channel bandwith bandwidth video bitrate should be managed while capturing WebRTC stream in browser. WCS server allows to limit minimum and maximum video bitrate for stream published. Audio bitrate is not managed.

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Now, bitrate increasing can be enforced in Chrome browser Chromium browsers only by setting x-google-max-bitrate and  x-google-min-bitrate parameters via SDP hook.
It is impossible to enforce bitrate rising with client and server settings, only bitrate decreasing can be managed.
In this case, Chrome specific settings take precedence if they are set, i.e. constraints and server settings will be ignored. Note that Chrome default settings found by experience is

x-google-max-bitrate=2500

In the latest Chrome builds, the option videoContentHint: "motion" should be set when enforcing bitrate on browser side, because Chrome drops publishing bitrate in prefer to resolution when one of the other values is set

    session.createStream({
        name: streamName,
        display: localVideo,
        ...
        videoContentHint: "motion"
    }).publish();

Enforcing bitrate increasing in Chrome browser with server parameters

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These settings are intended for Chromium-based browsers and work with, e.g., Opera, Vivaldi and Yandex.Browser. Also, they are applied when iOS Safari 12 or newer is used. They do

Bitrate enforcing does not work with in Firefox and Edge.

Usage

Bitrate limiting in certain borders can be useful for example when publishing video to Safari browser subscribers. This browser is sensitive to bitrate jumps, in this case picture quality loses until freeze and browser hangs. It is recommended to stabilize bitrate when publishing streams for Safari viewers by setting narrow limits of bitrate change, for example

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In this case picture quality in Safari browser will be acceptable depending on channel bandwith bandwidth and state.

Bitrate rising needs to be enforced when publishsing publishing HD and 4K streams. In this case, Chrome browser is recommended for publishing.

Known issues

1. In lates latest Chrome versions (Chrome 75 for example) browser holds publishing bitrate on low limit x-google-min-bitrate when publishing WebRTC H264 stream

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