Quality/bandwidth ramping during first 25 seconds of broadcast

[AlanM]

When starting up the broadcast, the quality is often very pixelated and bandwidth usage is low. Over the span of about 25 seconds, the stream settles and finally begins broadcasting at a constant, high-quality level.
* This is with Chrome on Windows.

We've looked into Chrome-related options and I've seen a few posts that mention "bandwidth estimation" and REMB (Receiver Estimated Maximum Bitrate). I read an article that specifically tested changing the sdp offer message on Chrome to use the new algorithm (old REMB vs new Transport Feedback). However, we did not see any changes when performing the same SDP update that worked for them. What we are looking for is an option to force an initial bandwidth level, so the stream goes to full quality more quickly (a few seconds). We've tested some other RTC demos (local, not one-to-many) and those did not have as long of a ramp-up time as Flashphoner. Is there an option either on the server side for WCS or the flashphoner client library to help with this issue?

 

[Max]

Hello

As you mentioned WCS uses REMB to control incoming bitrate.

We've tested some other RTC demos (local, not one-to-many) and those did not have as long of a ramp-up time as Flashphoner

Default range is:

#30 kbps
webrtc_cc_min_bitrate = 30000
#10 Mbps
webrtc_cc_max_bitrate = 10000000

https://docs.flashphoner.com/display/WCS5EN/Settings+file+flashphoner.properties

Therefore if actual bitrate is less than 30 kbps, WCS will not send REMB to reduce the bitrate.
You can lift up this threshold.

Example:

webrtc_cc_min_bitrate = 3000000

Then WCS will not reduce bitrate sending REMB packets.

If it does not help, it can be encoding issue.
Try to change codec to VP8 in flashphoner.properties
VP8 should have priority over H.264

codecs = ...vp8,h264...

We've tested some other RTC demos (local, not one-to-many) and those did not have as long of a ramp-up time as Flashphoner.

Did you check what video codec was used?
Generally VP8 can be used by default. This codec starts with high bitrate immediately.