polling-based active video approach

src/view/com/util/post-embeds/ActiveVideoContext.tsx

@@ -6,29 +6,56 @@ import React, {
   useRef,
   useState,
 } from 'react'
+import {useWindowDimensions} from 'react-native'
 
 import {VideoPlayerProvider} from './VideoPlayerContext'
 
 const ActiveVideoContext = React.createContext<{
   activeViewId: string | null
   setActiveView: (viewId: string, src: string) => void
-  requestActive: (viewId: string, src: string, y: number) => void
-  allowUsurp: (viewId: string) => void
+  registerMeasurementCallback: (
+    viewId: string,
+    callback: () => DOMRectReadOnly | void,
+  ) => {remove: () => void}
 } | null>(null)
 
 export function ActiveVideoProvider({children}: {children: React.ReactNode}) {
   const [activeViewId, setActiveViewId] = useState<string | null>(null)
   const [source, setSource] = useState<string | null>(null)
+  const {height: windowHeight} = useWindowDimensions()
 
-  const [canBeUsurped, setCanBeUsurped] = useState(false)
-  const requestedViews = useRef<{[key: string]: {src: string; y: number}}>({})
-  const timeoutRef = useRef<ReturnType<typeof setTimeout>>()
+  const measurementCallbacks = useRef<Record<string, () => DOMRect | void>>({})
 
   useEffect(() => {
-    return () => {
-      clearTimeout(timeoutRef.current)
+    const findAndActivateVideo = () => {
+      if (Object.keys(measurementCallbacks.current).length === 0) {
+        return
+      }
+
+      const locations = Object.entries(measurementCallbacks.current).map(
+        ([id, callback]) => ({
+          id,
+          rect: callback(),
+        }),
+      )
+
+      const videosInView = locations.filter(
+        ({rect}) => rect && rect.top >= 0 && rect.bottom <= windowHeight,
+      )
+
+      const active = closestToMiddle(windowHeight, videosInView)
+
+      if (active) {
+        setActiveViewId(active.id)
+      }
     }
-  }, [])
+    findAndActivateVideo()
+    const interval = setInterval(findAndActivateVideo, 1000)
+
+    return () => {
+      clearInterval(interval)
+    }
+  }, [activeViewId, windowHeight])
 
   const value = useMemo(
     () => ({
@@ -36,36 +63,17 @@ export function ActiveVideoProvider({children}: {children: React.ReactNode}) {
       setActiveView: (viewId: string, src: string) => {
         setActiveViewId(viewId)
         setSource(src)
-        setCanBeUsurped(false)
       },
-      requestActive: (viewId: string, src: string, y: number) => {
-        if (activeViewId && !canBeUsurped) {
-          return
-        }
-        if (requestedViews.current[viewId]) {
-          requestedViews.current[viewId].y = y
-          return
-        }
-        clearTimeout(timeoutRef.current)
-        requestedViews.current[viewId] = {src, y}
-        timeoutRef.current = setTimeout(() => {
-          const sortedViews = Object.entries(requestedViews.current).sort(
-            ([, {y: y1}], [, {y: y2}]) => y1 - y2,
-          )
-          const [topViewId, {src: topSrc}] = sortedViews[0]
-          setActiveViewId(topViewId)
-          setSource(topSrc)
-          setCanBeUsurped(false)
-          requestedViews.current = {}
-        }, 100)
-      },
-      allowUsurp: (viewId: string) => {
-        if (activeViewId === viewId) {
-          setCanBeUsurped(true)
+      registerMeasurementCallback: (viewId: string, callback: () => void) => {
+        measurementCallbacks.current[viewId] = callback
+        return {
+          remove: () => {
+            delete measurementCallbacks.current[viewId]
+          },
         }
       },
     }),
-    [activeViewId, canBeUsurped],
+    [activeViewId],
   )
 
   return (
@@ -77,23 +85,59 @@ export function ActiveVideoProvider({children}: {children: React.ReactNode}) {
   )
 }
 
-export function useActiveVideoView(source: string) {
+export function useActiveVideoView({
+  source,
+  measure,
+}: {
+  source: string
+  measure: () => void
+}) {
   const context = React.useContext(ActiveVideoContext)
   if (!context) {
     throw new Error('useActiveVideo must be used within a ActiveVideoProvider')
   }
   const id = useId()
 
+  useEffect(() => {
+    const sub = context.registerMeasurementCallback(id, measure)
+    return () => {
+      sub.remove()
+    }
+  }, [context, id, measure])
+
   return {
     active: context.activeViewId === id,
     setActive: useCallback(
       () => context.setActiveView(id, source),
       [context, id, source],
     ),
-    requestActive: useCallback(
-      (y: number) => context.requestActive(id, source, y),
-      [context, id, source],
-    ),
-    allowUsurp: useCallback(() => context.allowUsurp(id), [context, id]),
   }
 }
+
+function closestToMiddle(
+  windowHeight: number,
+  elements: {id: string; rect: DOMRect | void}[],
+) {
+  // actually gonna target 1/3 of the way down the screen
+  // so that the top post probably is the one that gets activated
+  const middle = windowHeight / 3
+  let closest = elements[0]
+
+  for (const element of elements) {
+    if (!element.rect) {
+      continue
+    }
+    if (!closest.rect) {
+      closest = element
+      continue
+    }
+    if (
+      Math.abs(element.rect.top + element.rect.height / 2 - middle) <
+      Math.abs(closest.rect.top + closest.rect.height / 2 - middle)
+    ) {
+      closest = element
+    }
+  }
+
+  return closest
+}

src/view/com/util/post-embeds/VideoEmbed.tsx

@@ -11,7 +11,7 @@ import {VideoEmbedInner} from './VideoEmbedInner'
 
 export function VideoEmbed({source}: {source: string}) {
   const t = useTheme()
-  const {active, setActive} = useActiveVideoView(source)
+  const {active, setActive} = useActiveVideoView({source, measure: () => {}})
   const {_} = useLingui()
 
   const onPress = useCallback(() => setActive(), [setActive])

src/view/com/util/post-embeds/VideoEmbed.web.tsx

@@ -1,4 +1,4 @@
-import React, {useEffect, useRef, useState} from 'react'
+import React, {useCallback, useEffect, useRef, useState} from 'react'
 import {View} from 'react-native'
 import Hls from 'hls.js'
 
@@ -8,12 +8,17 @@ import {useActiveVideoView} from './ActiveVideoContext'
 export function VideoEmbed({source}: {source: string}) {
   const [hls] = useState(() => new Hls())
   const hasLoaded = useRef(false)
-  const {active, setActive, requestActive, allowUsurp} =
-    useActiveVideoView(source)
   const ref = useRef<HTMLVideoElement>(null)
+  const {active, setActive} = useActiveVideoView({
+    source,
+    measure: useCallback(() => {
+      if (ref.current) {
+        return ref.current.getBoundingClientRect()
+      }
+    }, []),
+  })
   const t = useTheme()
 
-  // Use HLS.js to play HLS video
   useEffect(() => {
     if (ref.current && active && !hasLoaded.current) {
       hasLoaded.current = true
@@ -21,55 +26,22 @@ export function VideoEmbed({source}: {source: string}) {
         ref.current.src = source
       } else if (Hls.isSupported()) {
         hls.loadSource(source)
-        hls.attachMedia(ref.current)
       } else {
         // TODO: fallback
       }
     }
   }, [source, active, hls])
 
-  useEffect(() => {
-    return () => {
-      hls.destroy()
-    }
-  }, [hls])
-
   useEffect(() => {
     if (ref.current) {
-      const observer = new IntersectionObserver(
-        ([entry]) => {
-          if (ref.current) {
-            if (entry.intersectionRatio > 0.25) {
-              if (active) {
-                if (ref.current.paused) {
-                  ref.current.play()
-                }
-              } else {
-                requestActive(entry.boundingClientRect.y)
-              }
-            } else {
-              if (active) {
-                if (!ref.current.paused) {
-                  ref.current.pause()
-                }
-              }
-            }
-
-            if (entry.intersectionRatio < 0.75) {
-              allowUsurp()
-            }
-          }
-        },
-        {threshold: [0, 0.25, 1]},
-      )
-
-      observer.observe(ref.current)
-
-      return () => {
-        observer.disconnect()
+      if (
+        !ref.current.canPlayType('application/vnd.apple.mpegurl') &&
+        Hls.isSupported()
+      ) {
+        hls.attachMedia(ref.current)
       }
     }
-  }, [active, requestActive, allowUsurp])
+  }, [source, active, hls])
 
   return (
     <View