vycxexra8: Play feed videos from hlsUrl with a thumbnail fallback

src/lib/video-playback.ts

@@ -0,0 +1,21 @@
+// Chooses how a feed video plays. Pure, so it is unit-testable without a browser.
+
+export type Playback = "none" | "native" | "hlsjs";
+
+export interface PlaybackEnv {
+  /** True when the browser can play .m3u8 directly (Safari). */
+  nativeHls: boolean;
+  /** True when hls.js (Media Source Extensions) is supported. */
+  hlsJsSupported: boolean;
+}
+
+/** No hlsUrl: thumbnail only. Native HLS wins; hls.js is the fallback. */
+export function choosePlayback(hlsUrl: string | null | undefined, env: PlaybackEnv): Playback {
+  if (!hlsUrl) return "none";
+  if (env.nativeHls) return "native";
+  return env.hlsJsSupported ? "hlsjs" : "none";
+}
+
+export function supportsNativeHls(video: Pick<HTMLVideoElement, "canPlayType">): boolean {
+  return video.canPlayType("application/vnd.apple.mpegurl") !== "";
+}