The MediaElementAudioSourceNode interface represents an audio source consisting of an HTML <audio> or <video> element. It is an AudioNode that acts as an audio source.
A MediaElementAudioSourceNode has no inputs and exactly one output, and is created using the AudioContext.createMediaElementSource() method. The number of channels in the output equals the number of channels of the audio referenced by the HTMLMediaElement used in the creation of the node, or is 1 if the HTMLMediaElement has no audio.
Number of inputs
0
Number of outputs
1
Channel count
2 (but note that AudioNode.channelCount is only used for up-mixing and down-mixing AudioNode inputs, and MediaElementAudioSourceNode doesn't have any input)