use buffers for hasFrame (#5264)

app/packages/looker/src/lookers/utils.test.ts

@@ -0,0 +1,19 @@
+import { describe, expect, it } from "vitest";
+import type { Buffers } from "../state";
+import { hasFrame } from "./utils";
+
+describe("looker utilities", () => {
+  it("determines frame availability given a buffer list", () => {
+    const BUFFERS: Buffers = [
+      [1, 3],
+      [5, 25],
+    ];
+    for (const frameNumber of [1, 10, 25]) {
+      expect(hasFrame(BUFFERS, frameNumber)).toBe(true);
+    }
+
+    for (const frameNumber of [0, 4, 26]) {
+      expect(hasFrame(BUFFERS, frameNumber)).toBe(false);
+    }
+  });
+});

app/packages/looker/src/lookers/utils.ts

@@ -0,0 +1,7 @@
+import type { Buffers } from "../state";
+
+export const hasFrame = (buffers: Buffers, frameNumber: number) => {
+  return buffers.some(
+    ([start, end]) => start <= frameNumber && frameNumber <= end
+  );
+};

app/packages/looker/src/lookers/video.ts

@@ -19,6 +19,7 @@ import { addToBuffers, removeFromBuffers } from "../util";
 import { AbstractLooker } from "./abstract";
 import { type Frame, acquireReader, clearReader } from "./frame-reader";
 import { LookerUtils, withFrames } from "./shared";
+import { hasFrame } from "./utils";
 
 let LOOKER_WITH_READER: VideoLooker | null = null;
 
@@ -394,13 +395,7 @@ export class VideoLooker extends AbstractLooker<VideoState, VideoSample> {
   }
 
   private hasFrame(frameNumber: number) {
-    if (frameNumber === this.firstFrameNumber) {
-      return this.firstFrame;
-    }
-    return (
-      this.frames.has(frameNumber) &&
-      this.frames.get(frameNumber)?.deref() !== undefined
-    );
+    return hasFrame(this.state.buffers, frameNumber);
   }
 
   private getFrame(frameNumber: number) {