Audio Mixer: FAQ
From AVObjects Knowledge Base
q: The audio mixer is not implementing the iseekable interface. When I add the
mixer to a graph where seeking is currently enabled, the addition of the
mixer removes the graph's ability to seek. Also, when I wrote a source
filter that was using the interface, the mixer was not passing seek requests
to its pin.
a: Output pins of Audio Mixer filter supports IMediaSeeking. Please, see graph on attached picture. Seeking can be not supported only if some connected upstream filter not support it.