...
For optimal picture quality with available channel 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.
WCS builds before 5.2.1825 use REMB to manage a publishing bitrate. Since build 5.2.1825 TWCC is used by default.
Platforms and browsers supported
Chrome | Firefox | Safari 11 | Edge | |
|---|---|---|---|---|
Windows | + | + | + | |
Mac OS | + | + | + | |
Android | + | + | ||
iOS | - | - | + |
Settings
REMB
Since build 5.2.1825 REMB support should be enabled by the following parameter
| Code Block | ||
|---|---|---|
| ||
webrtc_cc2_twcc=false |
The following WCS settings are intended to limit publishing bitrate:
...
These settings work in most modern browsers and define the REMB bitrate management limits.
How it works
If maxBitrate is set, WCS server will send REMB command to decrease bitrate when this limit is reached.
If minBitrate is set, WCS server will stop sending REMB command to decrease bitrate when this limit is reached.
Therefore, the settings define 3 ranges with its own bitrate management algorithm:
| № | Range | Algorithm |
|---|---|---|
| 1 | [0, minBitrate] | WCS stops bitrate management and not send any REMB commands |
| 2 | [minBitrate, maxBitrate] | WCS server makes active bitrate management: depending on jitter and incoming traffic uniformity WCS decides to send REMB commands to decrease bitrate. If channel is good, WCS does nothing and bitrate is not decreasing |
| 3 | [maxBitrate, ...] | WCS constantly sends bitrate decrease commands until it reduce to maxBitrate |
TWCC
Since build 5.2.1825, TWCC is enabled by default
| Code Block | ||
|---|---|---|
| ||
webrtc_cc2_twcc=true |
When TWCC is used, bitrate may be limited via publishing constraints at browser side only, in kbps
| Code Block | ||||
|---|---|---|---|---|
| ||||
constraints.video.minBitrate=500 constraints.video.maxBitrate=1000 |
TWCC bitrate settings work in Android SDK 1.1.0.62, iOS SDK 2.6.122 and WebSDK 2.0.239.
How to enforce bitrate increasing
...