Currently with the RtpEncodingParameters the active field is supported
per simulcast layer, but max_bitrate_bps and bitrate_priority are just
supoorted per rtp sender. Updated the comments to make this more clear
and added TODOs with bugs.
Bug: webrtc:8819
Change-Id: I130f6dda0896079b5082af58a2693b898d6e22f0
Reviewed-on: https://webrtc-review.googlesource.com/52141
Reviewed-by: Taylor Brandstetter <deadbeef@webrtc.org>
Commit-Queue: Seth Hampson <shampson@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#22007}