Sprints: [WebAPI] Web Audio API docs tasks, Fx 70

[chrisdavidmills]

Trello: https://trello.com/c/z7uW1xc5/103-web-audio-api-fx-70

Acceptance criteria

1. 
   
   • [x] [Implement AudioContext getOutputTimestamp()](https://bugzilla.mozilla.org/show_bug.cgi?id=1324545)
   
   
2. 
   
   • [x] [Implement BaseAudioContext baseLatency and outputLatency attributes](https://bugzilla.mozilla.org/show_bug.cgi?id=1324552)
   
   
3. 
   
   • [x] [Implement new attributes MediaStreamAudioSourceNode and MediaElementAudioSourceNode](https://bugzilla.mozilla.org/show_bug.cgi?id=1350973)
   
   
4. 
   
   • [x] [ChannelMergerNode constructor should throw errors](https://bugzilla.mozilla.org/show_bug.cgi?id=1456263)
   
   

[chrisdavidmills]

getOutputTimestamp() covered:

• https://wiki.developer.mozilla.org/en-US/docs/Web/API/AudioContext
• https://wiki.developer.mozilla.org/en-US/docs/Web/API/AudioContext/getOutputTimestamp
• https://developer.mozilla.org/en-US/docs/Mozilla/Firefox/Releases/70#APIs
• BCD added: https://github.com/mdn/browser-compat-data/pull/5013

[padenot]

Chris, this documentation looks good to me, thanks!

[chrisdavidmills]

cheers @padenot! I'll finish off the rest of these docs tasks on Monday.

[chrisdavidmills]

baseLatency and outputLatency covered:

• https://developer.mozilla.org/en-US/docs/Web/API/AudioContext
• https://developer.mozilla.org/en-US/docs/Web/API/AudioContext/baseLatency
• https://developer.mozilla.org/en-US/docs/Web/API/AudioContext/outputLatency
• Compat data updated: https://github.com/mdn/browser-compat-data/pull/5019

[chrisdavidmills]

ChannelMergerNode docs completed:

• Rel note added to https://wiki.developer.mozilla.org/en-US/docs/Mozilla/Firefox/Releases/70#APIs
• Exceptions section added to the constructor page: https://wiki.developer.mozilla.org/en-US/docs/Web/API/ChannelMergerNode/ChannelMergerNode#Exceptions

[chrisdavidmills]

mediaStream and mediaElement docs sorted out:

• BCD updated: https://github.com/mdn/browser-compat-data/pull/5096
• Rel notes: https://wiki.developer.mozilla.org/en-US/docs/Mozilla/Firefox/Releases/70#APIs
• https://wiki.developer.mozilla.org/en-US/docs/Web/API/MediaStreamAudioSourceNode
• https://wiki.developer.mozilla.org/en-US/docs/Web/API/MediaStreamAudioSourceNode/mediaStream
• https://wiki.developer.mozilla.org/en-US/docs/Web/API/MediaElementAudioSourceNode
• https://wiki.developer.mozilla.org/en-US/docs/Web/API/MediaElementAudioSourceNode/mediaElement