Meet.jit.si: Sharing a video in a Chromium tab on Linux is unusable

As part of my Jul 6th 6:30PM-8PM EDT event with about 15 participants to give Jitsi a severe test, I tried sharing a local video file in a Chromium tab. I am using Chromium 83.0.4103.116-1~deb10u2 on Debian Linux 10.4 (Buster).

When I first tried it, everyone complained that video frames were dropping and audio was skipping too. I asked everyone to turn off their video, I left the conference and came back in. Video was still losing too many frames to be useful and audio was almost but not quite useable according to the reports I heard.

Here is what ffmpeg reports about the video:
Duration: 00:05:27.13, start: 0.000000, bitrate: 290 kb/s
Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 480x270 [SAR 1:1 DAR 16:9], 156 kb/s, 29.97 fps, 29.97 tbr, 30k tbn, 59.94 tbc (default)
Metadata:
handler_name : VideoHandler
Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 125 kb/s (default)