[Webkit-unassigned] [Bug 190349] New: Web Audio getByteFrequencyData fails in the context of a WebRTC call with G.711 codec

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=190349

            Bug ID: 190349
           Summary: Web Audio getByteFrequencyData fails in the context of
                    a WebRTC call with G.711 codec
           Product: WebKit
           Version: Safari 11
          Hardware: Unspecified
                OS: macOS 10.13
            Status: NEW
          Severity: Minor
          Priority: P2
         Component: Web Audio
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: philippe.sultan at gmail.com

Created attachment 351777

  --> https://bugs.webkit.org/attachment.cgi?id=351777&action=review

Diff that removes all audio codecs from SDP but PCMA / PCMU, computes FFT frequencies root mean square (RMS)

When you configure a WebRTC PeerConnection to use G.711 only (PCMU or PCMA), using any of the Web Audio API functions that compute FFT frequency coefficients on the remote stream does nothing.

Web Audio API functions are :
- getByteFrequencyData()
- getByteTimeDomainData()
- getFloatFrequencyData()
- getFloatTimeDomainData()

The following test page shows the problem :
https://codepen.io/phsultan/pen/PybLQr

With Chrome or Firefox, if you click Start then Call, the right pane will display both frequency + time domain charts in real time for the remote stream, thus giving an view of the signal power for the narrowband G.711 codec.

If you try the same with Safari, you would not see any activity on the right pane, and the JavaScript console shows that any array filled with the Web Audio API functions are filled with zero values.

The same test made with Opus works ok with Safari too, as shown in https://webrtc.github.io/samples/src/content/peerconnection/webaudio-output/. The above Codepen is based on the corresponding Github repo at https://github.com/webrtc/samples/tree/gh-pages/src/content/peerconnection/webaudio-output (diff attached).

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