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RTC event log

Overview

RTC event logs can be enabled to capture in-depth inpformation about sent and received packets and the internal state of some WebRTC components. The logs are useful to understand network behavior and to debug issues around connectivity, bandwidth estimation and audio jitter buffers.

The contents include:

  • Sent and received RTP headers
  • Full RTCP feedback
  • ICE candidates, pings and responses
  • Bandwidth estimator events, including loss-based estimate, delay-based estimate, probe results and ALR state
  • Audio network adaptation settings
  • Audio playout events

Binary wire format

No guarantees are made on the wire format, and the format may change without prior notice. To maintain compatibility with past and future formats, analysis tools should be built on top of the provided rtc_event_log_parser.h

In particular, an analysis tool should not read the log as a protobuf.

Visualization

Since the logs contain a substantial amount of data, it is usually convenient to get an overview by visualizing them as a set of plots. Use the command:

out/Default/event_log_visualizer /path/to/log_file | python

This visualization requires matplotlib to be installed. The tool is capable of producing a substantial number of plots, of which only a handful are generated by default. You can select which plots are generated though the --plot= command line argument. For example, the command

out/Default/event_log_visualizer \
  --plot=incoming_packet_sizes,incoming_stream_bitrate \
  /path/to/log_file | python

plots the sizes of incoming packets and the bitrate per incoming stream.

You can get a full list of options for the --plot argument through

out/Default/event_log_visualizer --list_plots /path/to/log_file

You can also synchronize the x-axis between all plots (so zooming or panning in one plot affects all of them), by adding the command line argument --shared_xaxis.

Viewing the raw log contents as text

If you know which format version the log file uses, you can view the raw contents as text. For version 1, you can use the command

out/Default/protoc --decode webrtc.rtclog.EventStream \
  ./logging/rtc_event_log/rtc_event_log.proto < /path/to/log_file

Similarly, you can use

out/Default/protoc --decode webrtc.rtclog2.EventStream \
  ./logging/rtc_event_log/rtc_event_log2.proto < /path/to/log_file

for logs that use version 2. However, note that not all of the contents will be human readable. Some fields are based on the raw RTP format or may be encoded as deltas relative to previous fields. Such fields will be printed as a list of bytes.