How to record audio on devices where no 3.5mm audio output

[yanj-github]

Test and document "How to record audio on devices where no 3.5mm audio output". Possible solutions:

• via SP DIP
• via HDMI ARC

[yanj-github]

• Tested and HDMI ARC can be used. It has same level of PASS/FAIL compared with 3.5mm audio. No delays noticed on HDMI ARC.
• SP DIP added some noise to the signal and which caused the audio observation to fail. Not suggested.

[jpiesing]

@Nicholas-fr

[yanj-github]

Document added on wiki: https://github.com/cta-wave/device-observation-framework/wiki/How-to-jointly-record-audio-and-video-(audio-only-%C2%A78-tests-and-%C2%A79-tests)

[nicholas-fr]

Regarding HDMI ARC and S/PDIF out (TOSLINK optical or RCA/coax), aside from some limited exceptions, they usually carry the same digital audio signal, so it should be possible to use either.

The DUT should be configured to ensure that:

• The digital audio out is uncompressed stereo (not bitstream).
• The digital audio out is configured to be in sync with video (normally the default).
• The correct audio output is selected (ARC and S/PDIF outputs can be mutually exclusive on some devices).
• If using ARC, both ARC and HDMI CEC functionality should be enabled, as CEC is required to initiate ARC.

Any transients/noise in the recording suggest issues with the setup, but should not be an issue inherent to S/PDIF.

It may be useful to add some of these details to the document.