Today, the WebRTC Telemetry tests are using the fake video device (green background with a moving circle) using the --use-fake-device-for-media-stream in the current WebRTC telemetry tests [1]. In order to get a video that is closer to a real-world scenario to encode and decode, we should use the --use-file-for-fake-video-capture flag to specify a prerecorded .yuv video instead.

This will require making sure to have the video downloaded to the host that runs the telemetry test (which shouldn't be too hard given that many other tests use .sha1 files for specifying resources to be downloaded from Google storage).

[1]: https://cs.chromium.org/chromium/src/tools/perf/measurements/webrtc.py?rcl=0&l=38