refactor(mediabunny): [PKG-MB-05] own video iterators, frame pools and rendering

packages/artplayer-proxy-mediabunny/src/video-frames.ts

@@ -0,0 +1,37 @@
+import type { WrappedCanvas } from 'mediabunny'
+
+export type FrameIterator = Pick<AsyncGenerator<WrappedCanvas, void, unknown>, 'next' | 'return'>
+const closing = new WeakMap<FrameIterator, Promise<void>>()
+const reading = new WeakMap<FrameIterator, Promise<WrappedCanvas | null>>()
+
+export function releaseIterator(iterator: FrameIterator | null): Promise<void> {
+  if (!iterator)
+    return Promise.resolve()
+  const previous = closing.get(iterator)
+  if (previous)
+    return previous
+  const pending = Promise.resolve().then(() => iterator.return()).then(() => {})
+  closing.set(iterator, pending)
+  return pending
+}
+
+export function readCanvas(iterator: FrameIterator): Promise<WrappedCanvas | null> {
+  const previous = reading.get(iterator)
+  if (previous)
+    return previous
+  const pending = Promise.resolve().then(() => iterator.next()).then(result => result.value ?? null)
+  reading.set(iterator, pending)
+  const clear = () => {
+    if (reading.get(iterator) === pending)
+      reading.delete(iterator)
+  }
+  pending.then(clear, clear)
+  return pending
+}
+
+export function frameAction(timestamp: number, time: number, dropLateFrames: boolean, avSyncTolerance: number, playbackRate: number): 'skip' | 'draw' | 'queue' {
+  const tolerance = dropLateFrames ? Math.max(0.06, avSyncTolerance / Math.max(1, playbackRate)) : 0
+  if (dropLateFrames && timestamp < time - tolerance)
+    return 'skip'
+  return timestamp <= time + tolerance ? 'draw' : 'queue'
+}