docs(subtitles): describe in-stream subtitles on converted playback

src/content/docs/docs/running-a-server/transcode-nodes.md

@@ -74,3 +74,5 @@ To change a transcode node's encoder, select the pencil in the node's header, se
 To make a node re-read its configuration straight away, use force reload in the [admin API](/docs/api): `POST /api/v2/admin/nodes/{id}/force-reload` for one node, or `POST /api/v2/admin/nodes/force-reload` for every enabled node. There is no button for it. On a transcode node it also ends every live playback session.
 
 Update all nodes together with the main server when the release notes say so. During the [1.0 update](/docs/updates#moving-from-alpha-to-10), don't mix alpha and 1.0 nodes.
+
+A transcode node on an older version than the main server can't send subtitles from inside a video file along with the converted video. Silo then converts that playback on the main server or an updated node instead. Only if **Node routing** leaves no such machine does an older node convert it, and the apps then download the subtitle separately, which can take minutes on network storage.

src/content/docs/docs/using-silo/subtitles.md

@@ -17,6 +17,12 @@ While a title is playing, open the subtitle list and choose a track:
 Choose **Off** to hide subtitles. The same language can appear more than
 once when the title has several subtitle tracks in that language.
 
+When Silo converts the video for your device, the mobile and TV apps get a
+text subtitle from inside the video file along with the video, so it appears
+as soon as playback starts. Turning on a subtitle from inside the file, or
+switching to another one, restarts the video at the same spot, which takes a
+moment.
+
 If the language you want isn't there,
 [find, upload, or generate subtitles](/docs/missing-subtitles).