Video freezing issues, how to analyze the log files?

[Jonathan Stewart]

[referred here from chromium-discuss]

I'm supporting a WebRTC based call center application for a client and they are seeing irregular but recurring video freezing during calls. I'm told it freezes for 10-20 seconds and recovers and that there is no issue with the audio when it does this. I have the logs from several occurrences gathered via webrtc-internals but I haven't been able to find any tools to parse them or help me analyze them. What else can I do to help determine the cause of the video freezing? Is there additional logging of some kind, WebRTC events that I should be listening to for buffer underrun and the like in the application, filing a bug with the logs I have, etc? 

I don't have the version numbers handy but I'm told it happened with both release and beta channel versions as of March 29th.

Thanks,

Jonathan

[Iñaki Baz Castillo]

2017-04-10 18:57 GMT+02:00 Jonathan Stewart <jonst...@gmail.com>:
> I'm supporting a WebRTC based call center application for a client and they
> are seeing irregular but recurring video freezing during calls. I'm told it
> freezes for 10-20 seconds and recovers and that there is no issue with the
> audio when it does this. I have the logs from several occurrences gathered
> via webrtc-internals but I haven't been able to find any tools to parse them
> or help me analyze them. What else can I do to help determine the cause of
> the video freezing? Is there additional logging of some kind, WebRTC events
> that I should be listening to for buffer underrun and the like in the
> application, filing a bug with the logs I have, etc?

Video gets frozen when packet loss happens. The browser asks for lost
packets via RTCP NACK messages but, sometimes due to network
congestion, the sender cannot even resend them. In that case, the
receiver browser sends a PLI or FIR to ask for a video full frame. It
may take 20-30 seconds before that happens.

If using Chrome, check chrome://webrtc-internals and look for "packet
loss" and "PLI count" on the video receiver.


--
Iñaki Baz Castillo
<i...@aliax.net>

[ebu...@cafex.com]

I'm seeing freezing in the current version too. It appears to happen when there is very irregular loss of a couple of packets (very slightly congested wifi for example). I've just reproduced it using apprtc calling someone else in my office, and it NACKs when freezes happen, and mostly recovers without a PLI. It looks like the buffers are set too short to allow for even a couple of milliseconds for the NACK response, which is far lower than pretty much any call over the internet. The graph I have shows the jitter buffer gets very small until loss, and I guessing they've changed it's minimum size.

I'm going to have a search through bug to see if it's raised already, and if not raise it.

Simulating any regular packet loss gets rid of the freezing as I'm guessing the jitter buffer stays large enough for the NACKs to actually get responses.

Eric

[Philip Eliasson]

Hi Jonathan/Eric!

It would be great if you could record an RTC event log when this happens. To do that go to chromium://webrtc-internals and click the "Create Dump" arrow, and then check the "Enable diagnostic packet and event recording" tickbox. Now make a call and the RTC event log will be dumped to the folder you selected. You can then upload the logs to the bug I created: https://bugs.chromium.org/p/webrtc/issues/detail?id=7489

Also, which version of chrome are you using? :) 

[ebu...@cafex.com]

Sorry for the delay in replying, I was on holiday. I'll try get those logs attached ASAP, though I'm not in the office today so it'll be a bit harder. I raised https://bugs.chromium.org/p/webrtc/issues/detail?id=7482 which has screenshots of webrtc internal graphs.

I'm was using 57.0.2987.133 (64-bit) on Linux, but the same happened with 57 versions on Windows and Mac.