# still being worked on, some of this is proven and some is not, see below
what this is supposed to do
An oscilloscope for comparing two audio sources in real time, a local file or a YouTube video against the phone mic, showing exactly how far apart they are and whether they are drifting. Version 2 adds a direct feed from Offset Listener, so instead of manually loading and matching a video, this page can ask Offset Listener what song is playing nearby right now and load it already synced.
what's real and tested versus still rough
The scope views, correlation, offset and residual measurement, and the manual file-versus-mic and video-versus-mic comparisons are the original working core of this tool. The Offset Listener auto-sync path is new, it depends on Offset Listener's own location-based sync working correctly first, and hasn't been exercised widely yet.
technologies and services involved
The Web Audio API for capturing and analyzing both channels locally, the YouTube IFrame API for the video path, and Offset Listener's own public sync data, read directly from offset-listener.vercel.app, for the auto-sync path.
the thinking behind it
Offset Listener claims two phones are in sync. This tool is the way to actually see that claim measured against a real microphone instead of taking it on faith.
One tap and it listens, identifies, loads a reference copy, finds the spot, and keeps it locked to the room on its own, logging every step.
Offset
--
waiting
Residual
--
Match
--
-50 msmic early | mic late+50 ms
Channel 1, local file
No file loaded
0:00 / 0:00
Channel 2, microphone
Mic off
YouTube, heard through the mic
Uses your rough location to find whatever song Offset Listener has synced nearby, and keeps this video locked to it automatically.
Paste a link, load it, then turn the mic on.
Play the song on channel 1 while the same song plays through a speaker or another device near the mic. Offset shows how far the mic trails the file. Align now delays the leading channel so both line up, and X-Y draws a thin diagonal line when they match. Press any control or screen to reveal its i button for a few seconds.