WebRTC congestion control (#26)

* Add congestion control

* Improve stream matching, add manual stream selection, add metrics

* Use a ticker for bitrate estimation and make bandwidth drops switch to lower streams more aggressively

* Missing signal response, fix video auto bug

* Remove redundant mutex

* Bitrate history queue

* Get bitrate fn support h264 & float64

---------

Co-authored-by: Aleksandar Sukovic <aleksandar.sukovic@gmail.com>

internal/capture/buckets/queue_test.go

@@ -0,0 +1,99 @@
+package buckets
+
+import "testing"
+
+func Queue_normaliseBitrate(t *testing.T) {
+	type fields struct {
+		queue *queue
+	}
+	type args struct {
+		currentBitrate int
+	}
+	tests := []struct {
+		name   string
+		fields fields
+		args   args
+		want   []int
+	}{
+		{
+			name: "normaliseBitrate: big drop",
+			fields: fields{
+				queue: &queue{
+					q: []elem{
+						{bitrate: 900},
+						{bitrate: 750},
+						{bitrate: 780},
+						{bitrate: 1100},
+						{bitrate: 950},
+						{bitrate: 700},
+						{bitrate: 800},
+						{bitrate: 900},
+						{bitrate: 1000},
+						{bitrate: 1100},
+						// avg = 898
+					},
+				},
+			},
+			args: args{
+				currentBitrate: 350,
+			},
+			want: []int{816, 700, 537, 350, 350},
+		}, {
+			name: "normaliseBitrate: small drop",
+			fields: fields{
+				queue: &queue{
+					q: []elem{
+						{bitrate: 900},
+						{bitrate: 750},
+						{bitrate: 780},
+						{bitrate: 1100},
+						{bitrate: 950},
+						{bitrate: 700},
+						{bitrate: 800},
+						{bitrate: 900},
+						{bitrate: 1000},
+						{bitrate: 1100},
+						// avg = 898
+					},
+				},
+			},
+			args: args{
+				currentBitrate: 700,
+			},
+			want: []int{878, 842, 825, 825, 812, 787, 750, 700},
+		}, {
+			name: "normaliseBitrate",
+			fields: fields{
+				queue: &queue{
+					q: []elem{
+						{bitrate: 900},
+						{bitrate: 750},
+						{bitrate: 780},
+						{bitrate: 1100},
+						{bitrate: 950},
+						{bitrate: 700},
+						{bitrate: 800},
+						{bitrate: 900},
+						{bitrate: 1000},
+						{bitrate: 1100},
+						// avg = 898
+					},
+				},
+			},
+			args: args{
+				currentBitrate: 1350,
+			},
+			want: []int{943, 1003, 1060, 1085},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			m := tt.fields.queue
+			for i := 0; i < len(tt.want); i++ {
+				if got := m.normaliseBitrate(tt.args.currentBitrate); got != tt.want[i] {
+					t.Errorf("normaliseBitrate() [%d] = %v, want %v", i, got, tt.want[i])
+				}
+			}
+		})
+	}
+}