Allow selection of different stream variants in the player (#815)

* WIP video quality selector

* The quality selector works even though it is not pretty

* Support getting and setting variant name. Closes #743

* Sort video qualities

* Fix odd looking selected states of menubutton items

* Fix comment

controllers/video.go

@@ -0,0 +1,45 @@
+package controllers
+
+import (
+	"net/http"
+	"sort"
+
+	"github.com/owncast/owncast/core/data"
+	"github.com/owncast/owncast/models"
+)
+
+type variants []models.StreamOutputVariant
+
+type variantsResponse struct {
+	Name  string `json:"name"`
+	Index int    `json:"index"`
+}
+
+// Len returns the number of variants.
+func (v variants) Len() int { return len(v) }
+
+// Less is less than..
+func (v variants) Less(i, j int) bool { return v[i].VideoBitrate < v[j].VideoBitrate }
+
+// Swap will swap two values.
+func (v variants) Swap(i, j int) { v[i], v[j] = v[j], v[i] }
+
+// GetVideoStreamOutputVariants will return the video variants available,
+func GetVideoStreamOutputVariants(w http.ResponseWriter, r *http.Request) {
+	outputVariants := data.GetStreamOutputVariants()
+	result := make([]variantsResponse, len(outputVariants))
+
+	for i, variant := range outputVariants {
+		variantResponse := variantsResponse{
+			Index: i,
+			Name:  variant.GetName(),
+		}
+		result[i] = variantResponse
+	}
+
+	sort.Slice(result, func(i, j int) bool {
+		return outputVariants[i].VideoBitrate > outputVariants[j].VideoBitrate || !outputVariants[i].IsVideoPassthrough
+	})
+
+	WriteResponse(w, result)
+}