6-7 secs video freeze with H.264 and 1920x1080 (Simucast=False)

[nwang0]

Issue:
When publishing video track using the python SDK, the video stream freezes for 6 to 7 seconds every 5 seconds.

My set up:

• Livekit cloud
• Tested with the hue demo script (https://github.com/livekit/python-sdks/blob/main/examples/publish_hue.py) running on a Macbook Pro M4
• Applied changes on top:
  • Increase resolution to 1920x1080
  • Increase bit rate to 8mbs
  • Disable Simucast
  • Use H.264 encoding
  • Use SOURCE_SCREENSHARE - The problem repro with SOURCE_CAMERA as well
• livekit package version 1.0.13

The result is observed in a livekit web client. However looking at the publishing stats, it stopped sending packets during the freeze regardless a client connected or not. In the stats, the qlim=2 which indicates a bandwidth issue. However I have confirmed that I have >200mbs internet connection.

One related issue (which is not obvious in this test) is that the video quality is significant lower comparing to the VP8 and VP9. The quality degradation is more than what normally expected from the codec difference.

Test with simucast off:
https://github.com/user-attachments/assets/0d431731-3a6d-4cfc-9ad1-2b5541b26562

Test with simucast on:
https://github.com/user-attachments/assets/b1c8e50a-af2a-49b9-a1b1-981afc8b353a

Note, the issue does not repro with the resolution of 1280x720.