Omit 'signal', clarify docs for reading ranged resources (#387)

docs/guide/reading-media-files.md

@@ -643,7 +643,11 @@ const source = new UrlSource('https://example.com/bigbuckbunny.mp4', {
 });
 ```
 
-All `requestInit` fields are respected except for `signal` and `headers.Range`, which are overridden by Mediabunny. The same applies to the `signal` and `headers.Range` values of a `Request` passed as the first constructor argument. To cancel ongoing requests, [dispose of the input](#disposing-inputs).
+::: info
+All `requestInit` fields are respected except for `signal` and `headers.Range`, which are overridden by Mediabunny. The same applies to the `signal` and `headers.Range` values of a `Request` passed as the first constructor argument.
+
+To cancel ongoing requests, [dispose of the input](#disposing-inputs). To load a specific range of the resource, create the `UrlSource` first and then call [`.slice()`](../api/Source#slice).
+:::
 
 `getRetryDelay` can be used to control the retry logic used should a request fail. When a request fails, `getRetryDelay` should return the time to wait in seconds before the request will be retried. Returning `null` prevents further retries.
 ```ts

src/source.ts

@@ -675,10 +675,13 @@ export type UrlSourceOptions = {
 	 * The [`RequestInit`](https://developer.mozilla.org/en-US/docs/Web/API/RequestInit) used by the Fetch API. Can be
 	 * used to further control the requests, such as setting custom headers.
 	 *
-	 * All fields will work except for `signal` and `headers.Range`; these will be overridden by Mediabunny. If you want
+	 * The `signal` field is not available, as Mediabunny controls request cancellation internally. If you want to
-	 * to cancel ongoing requests, use {@link Input.dispose}.
+	 * cancel ongoing requests, use {@link Input.dispose}.
+	 *
+	 * The `headers.Range` field will also be overridden by Mediabunny. For loading a ranged remote resource, create the
+	 * source, then call {@link Source.slice}.
 	 */
-	requestInit?: RequestInit;
+	requestInit?: Omit<RequestInit, 'signal'>;
 
 	/**
 	 * A function that returns the delay (in seconds) before retrying a failed request. The function is called