Show equalizer icon on amp-story videos containing sound

The audio icon is sometimes displayed even though the page does not have audio, and the audio icon is sometimes not displayed even though the page does have audio.

The definition we’re using for whether the page has audio is found in page-element.js (copied below):

mediaElement.mozHasAudio ||
        Boolean(mediaElement['webkitAudioDecodedByteCount']) ||
        Boolean(mediaElement.audioTracks && mediaElement.audioTracks.length);

This is not foolproof and doesn’t work cross-browser. We can instead use a ScriptProcessorNode in audio.js and check when audio is actually being produced by some source on the page, and display the icon at that time. At that time, we can also add a has-audio attribute or CSS class to the page so that we don’t have to recalculate this.

[dreamofabear]

@sanjsanj Feel free to give it a go! Let me know if you have any questions.

[sanjsanj]

Is this issue available to be picked up please? I’ve only done a GFI involving amp-story so far.