Add a default noise floor. (#13)

(Turns out not) Pretty simple, if the average amplitude is under a certain value clear
out the buffer! The value I chose (.001) was an arbitrary value I got
from printf debugging. I was able to show that this worked pretty well
on the desktop session. Hopefully we'll add this to the settings page at
some point.

Once the app has been under that threshold for more than 200ms, we stop transmitting and send a terminator packet.

Reviewed-on: #13
Reviewed-by: restitux <restitux@ohea.xyz>

gui/src/imp/native_audio.rs

@@ -1,4 +1,4 @@
-use crate::effects::{AudioProcessor, AudioProcessorSender};
+use crate::effects::{AudioProcessor, AudioProcessorSender, TransmitState};
 use color_eyre::eyre::{eyre, Error};
 use cpal::traits::{DeviceTrait, HostTrait, StreamTrait as _};
 use futures::io::{AsyncRead, AsyncWrite};
@@ -23,6 +23,31 @@ pub struct AudioSystem {
 const SAMPLE_RATE: u32 = 48_000;
 const PACKET_SAMPLES: u32 = 960;
 
+fn encode_and_send(
+    state: TransmitState,
+    output_buffer: &mut Vec<f32>,
+    encoder: &mut opus::Encoder,
+    each: &mut impl FnMut(Vec<u8>, bool),
+) {
+    let (is_terminator, should_encode) = match state {
+        TransmitState::Silent => return,
+        TransmitState::Transmitting => (false, output_buffer.len() >= PACKET_SAMPLES as usize),
+        TransmitState::Terminator => {
+            output_buffer.resize(PACKET_SAMPLES as usize, 0.0);
+            (true, true)
+        }
+    };
+
+    if should_encode {
+        let remainder = output_buffer.split_off(PACKET_SAMPLES as usize);
+        let frame = replace(output_buffer, remainder);
+        match encoder.encode_vec_float(&frame, frame.len() * 2) {
+            Ok(encoded) => each(encoded, is_terminator),
+            Err(e) => error!("error encoding {} samples: {e:?}", frame.len()),
+        }
+    }
+}
+
 type Buffer = Arc<Mutex<dasp_ring_buffer::Bounded<Vec<i16>>>>;
 
 impl AudioSystem {
@@ -79,7 +104,7 @@ impl AudioSystem {
 
     pub fn start_recording(
         &mut self,
-        mut each: impl FnMut(Vec<u8>) + Send + 'static,
+        mut each: impl FnMut(Vec<u8>, bool) + Send + 'static,
     ) -> Result<(), Error> {
         let config = self.choose_config(self.input.supported_input_configs()?)?;
         info!(
@@ -97,20 +122,8 @@ impl AudioSystem {
             if let Some(new_processor) = processors.take() {
                 current_processor = new_processor;
             }
-            current_processor.process(frame, config.channels as usize, &mut output_buffer);
-            if output_buffer.len() < PACKET_SAMPLES as usize {
-                return;
-            }
-            let remainder = output_buffer.split_off(PACKET_SAMPLES as usize);
-            let frame = replace(&mut output_buffer, remainder);
-            match encoder.encode_vec_float(&frame, frame.len() * 2) {
-                Ok(buf) => {
-                    each(buf);
-                }
-                Err(e) => {
-                    error!("error encoding {} samples: {e:?}", frame.len());
-                }
-            }
+            let state = current_processor.process(frame, config.channels as usize, &mut output_buffer);
+            encode_and_send(state, &mut output_buffer, &mut encoder, &mut each);
         };
 
         match self