Aligning/synchronizing live audio with pad.set_offset

Michiel Konstapel michiel at
Fri Apr 22 14:08:53 UTC 2022

On 21-04-2022 23:24, Michiel Konstapel wrote:
> I am trying to synchronize multiple (microphone) audio tracks picking 
> up the same sound, but currently testing using files as input; one 
> original and one copy delayed by a few dozen milliseconds. I am using 
> cross correlation based on to 
> calculate the required time shift to bring them into alignment. This 
> works, I get the exact amount to delay the "early" signal by.
> However, now I need to actually *apply* the delay to one of the 
> streams, before they go into an audiomixer. I am trying to do so using 
> pad.set_offset() either on the source pad of a queue that feeds into 
> the mixer (because I recall a comment that set_offset() must be called 
> on a source pad), or on the sinkpad of the audiomixer.
> If I do so before starting the pipeline, it works. But I want to do 
> this on the fly (live input) - but if I call set_offset() on a pad 
> while it is running, either nothing happens, or I very briefly get a 
> fragment of perfectly synced audio, and then (it sounds like) it just 
> goes back to the old timing.
> What should I do to apply a delay to an audiomixer input in a running 
> pipeline?
> Kind regards,
> Michiel

Looks like I have it working! I had a silly bug: I had a time in seconds 
and forgot to convert it to nanoseconds... while in another code path I 
did do the conversion, so *that* worked. Also, it works when setting the 
offset on the peer of the mixer sinkpad - so indeed on a source pad.

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