what would cause an appsink to double its new-sample callback rate?

[Andres Gonzalez]

Hi,

I have an audiomixer feeding an appsink which has the new-sample callback registered so my application gets the mixed audio samples. The audiomixer has its output-buffer-duration set for 1/30 and all of the mixer inputs are also feeding the audiomixer at 1/30 with 48kHz 16 bit, 2 channel audio. This gives a 6400 byte sample chunk every 33 msecs from the appsink new-sample callback.  

the pipeline is:

    audiomixer -> queue -> audioconvert -> audioresample -> appsink

This is working great for several mixer inputs and the appsink new-sample callback gets called every 33 msecs as expected. However, under certain inputs, the appsink new-sample callback gets called every 16 msecs instead of 33 msecs with the same amount of data. That is, it appears to generate twice the data since it is calling the callback twice as fast (all of the GstSample have 6400 bytes of data). This is not related to the number of mixer inputs since it appears to work correctly with several inputs configured.

The audiomixer does not change its output-buffer-duration even when the appsink is running twice as fast. I can read it and verify that it is as originally configured for 1/30.  I am assuming here that the audiomixer will only feed the downstream appsink at the rate configured by output-buffer-duration.  (All of the mixer inputs have an appsrc before the pad so all of the inputs are generic to the audiomixer.)

Question: is there anything that would cause appsink to double its new-sample callback rate?
Question: is there anything that would cause audiomixer to output data different from its configured output-buffer-duration?

Thanks,
-Andres