Can you send the output of chrome://webrtc-internals during this? 

Assigning to braveyao@ for repro/triage?

Please find attached. Many thanks for your assistance. 

Deleted: webrtc_internals_dump.txt 394 KB

webrtc_internals_dump.txt 394 KB View Download

Deleted: Gmail - dump1.pdf 89.0 KB

Gmail - dump1.pdf 89.0 KB Download

Deleted: Gmail - dump2.pdf 121 KB

Gmail - dump2.pdf 121 KB Download

Failed to reproduce the problem.
After step 5&6, the phone and desktop side are showing each own local preview. I suppose there should be a one-way video stream from desktop to phone, right?

the attached webrtc_internals_dump.txt shows a recvonly connection is established with VP8. There isn't much statistics, but encoded output is still 720P.

Could you please check the reproduction steps again?

And it's as expected that frame size will be downscaled under some circumstance, such as bandwidth is not enough or CPU usage is too high. 

Thanks for looking into the problem.

After step 5 - you're broadcasting your mobile camera to your desktop.

The intent is to create a broadcast stream that can be seen my many different users. We are producing an online auction platform with live video.

So, you're logged in one the mobile but not logged in on the desktop :)

(Mobile is streaming, and desktop is viewing)

It's not actually showing at 720p; when I use Firefox I see a higher quality output, but Firefox itself has a whole different set of issues! :)

Whilst I agree that it's expected that the frame size would downscale under some circumstances, I am using a 4G connection in Australia with perfect signal with plenty of bandwidth right by the Telstra pole and the CPU on the Samsung S7 is handling it with ease. So I am pretty confident that's not the issue. 

I think I understand your working scenario now and can set up a similar test  with appr.tc locally.

I tried Firefox on my Nexus5X. It seems that Firefox utilizes HW VP8, so it can keep working at 640x480@30fps if the connection is good. Meantime Firefox seems not using HW H264 yet.
If HW codec is enforced in Chrome, the frame size won't be downscaled too. But at present we enables HW h264 in Chrome, not VP8 yet. Maybe you can try H264 on Chrome instead?

Some basic truth:
With SW codec, the CPU power of phones won't be enough even for 640x480@30fps, definitely not for 720p. If bigger frame size with high frame rate is needed, using HW is kinda a must. But unfortunately, HW codec doesn't work well on all kinds of phones. Some compromise has to be made.
4G connection generally is worse than WiFi in most of the tests. Maybe you have a great LTE netowrk. But it's still normal you will see frame size downscale or frame rate drop. With HW codec involved, usually frame size will be kept while frame rate will be dropped to adapt to the current network condition.

As it works as intended, I'll close this as WontFix for now. Don't worry, we are working on HW codec on mobile device. Things will be better.