When developer wants to visualize audio playback position, there is no good way to achieve it, especially when playback speed is being varied (scrubbing playback position, making scratching noise etc.)
There could be a few approaches but how about having adding "playbackPosition" attribute to AudioBufferSourceNode? value could be either time in milliseconds or index number of sample arraybuffer.
*** Bug 61524 has been marked as a duplicate of this bug. ***