Capture bandwidth switch (#14)

* Handle bitrate change by finding the stream with closest bitrate as peer

* Convert video id into bitrate when creating peer or changing bitrate

* Try to fix prometheus panic

* Revert metrics label name change

* minor fixes.

* bitrate selector.

* skip if moving to the same stream.

* no closure for getting target bitrate.

* fix: high res switch to lo video, stream bitrate out of range

* revert dev config change.

* white space.

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

pkg/types/capture.go

@@ -22,7 +22,7 @@ type Sample media.Sample
 type Receiver interface {
 	SetStream(stream StreamSinkManager) error
 	RemoveStream()
-	OnVideoIdChange(f func(string) error)
+	OnBitrateChange(f func(int) error)
 }
 
 type BucketsManager interface {
@@ -46,6 +46,7 @@ type ScreencastManager interface {
 }
 
 type StreamSinkManager interface {
+	ID() string
 	Codec() codec.RTPCodec
 
 	AddListener(listener *func(sample Sample)) error
@@ -70,6 +71,8 @@ type CaptureManager interface {
 	Start()
 	Shutdown() error
 
+	GetBitrateFromVideoID(videoID string) (int, error)
+
 	Broadcast() BroadcastManager
 	Screencast() ScreencastManager
 	Audio() StreamSinkManager
@@ -83,6 +86,7 @@ type VideoConfig struct {
 	Width       string            `mapstructure:"width"`        // expression
 	Height      string            `mapstructure:"height"`       // expression
 	Fps         string            `mapstructure:"fps"`          // expression
+	Bitrate     int               `mapstructure:"bitrate"`      // pipeline bitrate
 	GstPrefix   string            `mapstructure:"gst_prefix"`   // pipeline prefix, starts with !
 	GstEncoder  string            `mapstructure:"gst_encoder"`  // gst encoder name
 	GstParams   map[string]string `mapstructure:"gst_params"`   // map of expressions
@@ -173,3 +177,41 @@ func (config *VideoConfig) GetPipeline(screen ScreenSize) (string, error) {
 		config.GstSuffix,
 	}[:], " "), nil
 }
+
+func (config *VideoConfig) GetBitrateFn(getScreen func() *ScreenSize) func() (int, error) {
+	return func() (int, error) {
+		if config.Bitrate > 0 {
+			return config.Bitrate, nil
+		}
+
+		screen := getScreen()
+		if screen == nil {
+			return 0, fmt.Errorf("screen is nil")
+		}
+
+		values := map[string]any{
+			"width":  screen.Width,
+			"height": screen.Height,
+			"fps":    screen.Rate,
+		}
+
+		language := []gval.Language{
+			gval.Function("round", func(args ...any) (any, error) {
+				return (int)(math.Round(args[0].(float64))), nil
+			}),
+		}
+
+		// TODO: This is only for vp8.
+		expr, ok := config.GstParams["target-bitrate"]
+		if !ok {
+			return 0, fmt.Errorf("target-bitrate not found")
+		}
+
+		targetBitrate, err := gval.Evaluate(expr, values, language...)
+		if err != nil {
+			return 0, err
+		}
+
+		return targetBitrate.(int), nil
+	}
+}