Any advice on a free "solution" to echo cancellation?

Question

Audio

Good afternoon.
I am working on a task in the implementation of which it is necessary to provide echo cancellation in the talk mode.
The peculiarity of the iron implementation implies serious delays - more than 400 ms, introducing distortions into the echo signal, as well as a tendency to "auto-disturbances".
At the moment I'm trying to use the C# filter port from WebRTC implemented by Startrinity. There is no result. Either the filter does not save from auto disturbance / echo, or does not pass the signal in principle.
If someone has experience using this port, can you tell me if it can be used with such delays between signals?
Otherwise, tell me, what free echo cancellation solution is worth / can be used in this case?

Answer 1

Have you tried AEC from Speex? Also, as an option, these guys can help - www.solicall.com