Thanks. Browser is Chrome 74, OS is Windows 10 x64. At least this is what I used for testing, I also have Opera on the same laptop which also writes to same SSLKEYLOG file. I tried to make a test from Opera now, I had the same result, Can't find master secret.

@MartinBonner yes, pardon me, I expressed myself badly. I meant the same, actual cipher suite is TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256 (0xc02b). But with this I'm still not sure how I would be able to get the video stream from WebRTC. Further complicates things that audio and video are in same stream, on same port.