Ideally this should check an actual return var of the function. I usually declare it with a different name to make sure it's the right one:

func (c *inboundCall) transferCall(...) (gerr error) {
	// ...
	defer func() {
		if gerr != nil {
			// ...
		}
	}()

Since w may contain C resampler, we need to make sure it's either set back via SwapOutput, or closed if it's no longer needed.

Sorry for confusing, but this still is not closed. The c.media.GetAudioWriter() is fine, it will be closed when c.media is closed. The problem is with w - you detach it from the room, so it won't be closed if the transfer succeeds. It should probably be in the defer below - it either swaps w back to the room, or should close it.