How to use buffer from AudioTransportSource as an input to AudioProcessorGraph

Hi I am new to JUCE. I tried passing the buffer from getNextAudioBlock() of AudioTransportSource to processBlock of custom class that uses AudioProcessorGraph and contain a simple plugin that should process my buffer. Any help is appreciated. Below is what I did.

Created an AudioTransportSource to play an audio file and passed the buffer from getNextAudioBlock to processBlock of next class.
The second class contains a volume controller plugin which should accept the buffer and give output.

Added AudioInputProcessor , plugin node, AudioOutputProcessor to graph.
Added connection information of graph from input to output .

Output : I am getting the audio played but plugin is ineffective
Desired output : Volume should be managed from plugin

PS: if I remove AudioInputProcessor, there is no output when I play audio file.

Thanks in advance

@moderators, Please help

@jules, Is it possible to use buffer from audio source and pass it to audioprocessor graph
e.g. output of mini player sample to Audio processor graph