fix(core): a clip that has fully downloaded stays loaded and plays on time

packages/core/src/runtime/preloadMedia.test.ts

@@ -116,6 +116,36 @@ describe("releasing a clip's download", () => {
     expect(video.getAttribute("src")).toBe("a.mp4");
   });
 
+  it("keeps a clip whose whole file is buffered", () => {
+    const video = document.createElement("video");
+    video.setAttribute("src", "a.mp4");
+    Object.defineProperty(video, "duration", { value: 6.67 });
+    Object.defineProperty(video, "buffered", {
+      value: { length: 1, start: () => 0, end: () => 6.67 },
+    });
+    video.load = vi.fn();
+
+    releaseMedia(video);
+    expect(video.load).not.toHaveBeenCalled();
+    expect(video.getAttribute("src")).toBe("a.mp4");
+  });
+
+  it.each([
+    [0, 15],
+    [430, 2642],
+  ])("releases a clip with only %s-%s s of a long file buffered", (from, to) => {
+    const video = document.createElement("video");
+    video.setAttribute("src", "a.mp4");
+    Object.defineProperty(video, "duration", { value: 2642 });
+    Object.defineProperty(video, "buffered", {
+      value: { length: 1, start: () => from, end: () => to },
+    });
+    video.load = vi.fn();
+
+    releaseMedia(video);
+    expect(video.load).toHaveBeenCalledTimes(1);
+  });
+
   it("leaves a clip on <source> children, their order and its markup untouched", () => {
     const video = document.createElement("video");
     video.innerHTML =

packages/core/src/runtime/preloadMedia.ts

@@ -5,6 +5,8 @@ import { defersMedia } from "./timedClipHide";
 import { swallow } from "./diagnostics";
 import { mediaElementTime } from "./mediaClock";
 
+const MEDIA_EDGE_SECONDS = 0.1;
+
 type PreloadableMedia = Pick<
   HTMLMediaElement,
   "id" | "tagName" | "getAttribute" | "preload" | "readyState" | "networkState" | "load"
@@ -73,8 +75,20 @@ export function stopMediaDownload(media: HTMLMediaElement): void {
   media.load();
 }
 
+// The whole file in memory: its download is over, so releasing it would free no connection, only drop the data.
+function wholeFileBuffered(media: HTMLMediaElement): boolean {
+  const { buffered, duration } = media;
+  return (
+    Number.isFinite(duration) &&
+    duration > 0 &&
+    buffered.length === 1 &&
+    buffered.start(0) <= MEDIA_EDGE_SECONDS &&
+    buffered.end(0) >= duration - MEDIA_EDGE_SECONDS
+  );
+}
+
 export function releaseMedia(media: HTMLMediaElement): void {
-  if (media.querySelector("source")) return;
+  if (media.querySelector("source") || wholeFileBuffered(media)) return;
   const src = media.getAttribute("src");
   stopMediaDownload(media);
   if (src !== null) media.setAttribute("src", src);