api: prepare caption-only services

api/src/processing/helpers/captions.js

@@ -1,5 +1,36 @@
 const normalizedLanguage = language => language?.toLowerCase().replace("_", "-");
 
+export const createCaptionResponse = ({
+    url,
+    format,
+    language,
+    service,
+    id,
+    title,
+    author,
+    source,
+    headers,
+}) => ({
+    type: "captions",
+    isCaptionOnly: true,
+    urls: url,
+    headers,
+    captionFormat: format,
+    captionLanguage: language,
+    filenameAttributes: {
+        service,
+        id,
+        title: title || `${service}_${id}`,
+        author,
+    },
+    captionMetadata: {
+        title,
+        author,
+        language,
+        source,
+    },
+});
+
 export const selectCaptionTrack = (tracks, subtitleLang, allowAutomatic = false) => {
     const allowed = tracks.filter(track => allowAutomatic || track.kind !== "asr");
     if (!allowed.length) return;

api/src/processing/match.js

@@ -7,6 +7,7 @@ import { testers } from "./service-patterns.js";
 import matchAction from "./match-action.js";
 
 import { friendlyServiceName } from "./service-alias.js";
+import { captionOnlyServices } from "./service-config.js";
 
 import bilibili from "./services/bilibili.js";
 import reddit from "./services/reddit.js";
@@ -66,7 +67,7 @@ export default async function({ host, patternMatch, params, authType }) {
             });
         }
 
-        if (isCaptionOnly && host !== "youtube") {
+        if (isCaptionOnly && !captionOnlyServices.has(host)) {
             return createResponse("error", {
                 code: "error.api.service.captions_not_supported"
             });

api/src/processing/service-config.js

@@ -1,6 +1,7 @@
 import UrlPattern from "url-pattern";
 
 export const audioIgnore = new Set(["vk", "ok", "loom"]);
+export const captionOnlyServices = new Set(["youtube"]);
 export const hlsExceptions = new Set(["dailymotion", "vimeo", "rutube", "bsky", "youtube"]);
 
 export const services = {

api/src/stream/captions.js

@@ -28,6 +28,7 @@ export default async function captions(streamInfo, res) {
             signal: abortController.signal,
             maxRedirections: 4,
             dispatcher: defaultAgent,
+            headers: streamInfo.headers,
         });
 
         if (response.statusCode < 200 || response.statusCode > 299) {

docs/api.md

@@ -95,10 +95,11 @@ all keys except for `url` are optional. value options are separated by `/`.
 | `youtubeBetterAudio`    | `boolean` | prefer higher quality youtube audio if possible   | `false` |
 | `youtubeHLS`            | `boolean` | use HLS formats when downloading from youtube     | `false` |
 
-#### standalone youtube captions
+#### standalone captions
 
 set `downloadMode` to `captions` to download a caption or transcript file without
-downloading video or audio. this mode currently supports youtube links.
+downloading video or audio. supported services are listed in the
+[api readme](/api/README.md#supported-services).
 
 `captionLanguage` selects the caption language, falling back to `subtitleLang` when
 omitted. if both are omitted, cobalt prefers the first manually provided track and

web/i18n/en/error/api.json

@@ -25,7 +25,7 @@
     "service.unsupported": "this service is not supported yet. have you pasted the right link?",
     "service.disabled": "this service is generally supported by cobalt, but it's disabled on this processing instance. try a link from another service!",
     "service.audio_not_supported": "this service doesn't support audio extraction. try a link from another service!",
-    "service.captions_not_supported": "standalone transcripts are only available for youtube links right now.",
+    "service.captions_not_supported": "this service doesn't support standalone transcripts.",
 
     "link.invalid": "your link is invalid or this service is not supported yet. have you pasted the right link?",
     "link.unsupported": "{{ service }} is supported, but i couldn't recognize your link. have you pasted the right one?",