BWE increases slowly when audio packets are sent before video packets.

src/bwe.rs

@@ -82,4 +82,16 @@ impl<'a> Bwe<'a> {
     pub fn set_desired_bitrate(&mut self, desired_bitrate: Bitrate) {
         self.0.session.set_bwe_desired_bitrate(desired_bitrate);
     }
+
+    /// Reset the BWE with a new init_bitrate
+    ///
+    /// # Example
+    ///
+    /// This method is useful when you initially start with only an audio stream. In this case, the BWE will report a very low estimated bitrate.
+    /// Later, when you start a video stream, the estimated bitrate will be affected by the previous low bitrate, resulting in a very low estimated bitrate, which can cause poor video stream quality.
+    /// To avoid this, you need to warm up the video stream for a while then calling reset with a provided init_bitrate.
+    ///
+    pub fn reset(&mut self, init_bitrate: Bitrate) {
+        self.0.session.reset_bwe(init_bitrate);
+    }
 }

src/packet/bwe/acked_bitrate_estimator.rs

@@ -73,8 +73,7 @@ impl AckedBitrateEstimator {
         // current estimate. With low values of uncertainty_symmetry_cap_ we add more
         // uncertainty to increases than to decreases. For higher values we approach
         // symmetry.
-        let sample_uncertainty =
-            scale * (estimate_bps - sample_estimate_bps).abs() / (estimate_bps.max(25_000.0));
+        let sample_uncertainty = scale * (estimate_bps - sample_estimate_bps).abs() / estimate_bps;
         let sample_var = sample_uncertainty.powf(2.0);
 
         // Update a bayesian estimate of the rate, weighting it lower if the sample
@@ -85,6 +84,7 @@ impl AckedBitrateEstimator {
         let mut new_estimate = (sample_var * estimate_bps
             + pred_bitrate_estimate_var * sample_estimate_bps)
             / (sample_var + pred_bitrate_estimate_var);
+
         new_estimate = new_estimate.max(ESTIMATE_FLOOR.as_f64());
         self.estimate = Some(Bitrate::bps(new_estimate.ceil() as u64));
         self.estimate_var =
@@ -136,7 +136,7 @@ impl AckedBitrateEstimator {
 
         self.sum += packet_size;
 
-        estimate.map(|e| (e, false))
+        estimate.map(|e| (e, is_small))
     }
 }
 
@@ -200,7 +200,7 @@ mod test {
 
         assert_eq!(
             estimate.as_u64(),
-            99530,
+            108320,
             "AckedBitrateEstiamtor should produce the correct bitrate"
         );
     }

src/session.rs

@@ -796,6 +796,12 @@ impl Session {
         }
     }
 
+    pub fn reset_bwe(&mut self, init_bitrate: Bitrate) {
+        if let Some(bwe) = self.bwe.as_mut() {
+            bwe.reset(init_bitrate);
+        }
+    }
+
     pub fn line_count(&self) -> usize {
         self.medias.len() + if self.app.is_some() { 1 } else { 0 }
     }
@@ -898,6 +904,10 @@ impl Bwe {
         self.bwe.handle_timeout(now);
     }
 
+    pub fn reset(&mut self, init_bitrate: Bitrate) {
+        self.bwe = SendSideBandwithEstimator::new(init_bitrate);
+    }
+
     pub fn update<'t>(
         &mut self,
         records: impl Iterator<Item = &'t crate::rtp_::TwccSendRecord>,