#Thumbnails

A still frame of every live stream, once a minute. Always visible to you; public only when you turn it on.

While a stream is live, JustOnAir takes one frame a minute from it: the first about 10 seconds after the publisher starts, then every 60 seconds. You always see the newest one; viewers and the public see it only if you make it public.

#Where you see it

thumbnail on the stream:

"thumbnail": {
  "public": false,
  "url": "https://live.joacdn.com/bcdn_token=…/_rec/str_e1bzk3dxw9z9allei6n7/thumbs/1791115200/thumb.jpg",
  "captured_at": "2026-10-04T12:00:00.000Z",
  "public_url": null
}

• url is a signed link to the newest frame, a 640-pixel-wide JPEG (360 pixels high for 16:9). It works for about an hour and opens that one frame only. Read the stream again for a fresh link; while nothing changes the link stays the same, so browsers can cache the image.
• captured_at is when the frame was taken. Both are null until the first frame.
• GET /v1/streams carries the same object on every stream, so one call gives you a picture for each row of your own stream list. The dashboard shows it in the stream list, as the poster of the live preview, and as the last frame of an ended stream.

#Make it public

Off by default. Turn it on when you create the stream or later:

curl -X PATCH https://api.justonair.com/v1/streams/str_e1bzk3dxw9z9allei6n7 \
  -H "Authorization: Bearer $JOA_API_KEY" -H "Content-Type: application/json" \
  -d '{"thumbnail": {"public": true}}'

Or with Public thumbnail in the dashboard's Stream settings. While it is on:

• The hosted player uses it. The newest frame is the video's poster before playback starts, and a blurred backdrop behind "Going live" and "Stream ended".
• public_url works for anyone:

https://play.joacdn.com/api/embed/str_e1bzk3dxw9z9allei6n7/thumbnail.jpg

It never changes; it redirects to the newest frame, or to the JustOnAir placeholder before the first one, so an <img> always has something to show. Use it for link previews (og:image), event pages, or your own list of live streams. It is cached for 30 seconds.

<img src="https://play.joacdn.com/api/embed/str_e1bzk3dxw9z9allei6n7/thumbnail.jpg"
  alt="Live now" width="640" height="360">

Turned off, the player shows no frame and public_url answers 404. The setting is separate from player.enabled: switching the hosted player off hides the poster, but the public thumbnail keeps working while it is on.

#How long frames are kept

Frames are stored with the stream's recording and deleted with it: when the recording reaches its delete_at, when you delete it, or, for a stream created with "record": false, a few minutes after the stream ends. Once they are gone url and captured_at are null, and a public thumbnail falls back to the placeholder.

#Things to know

• Leave it off for private streams. A public thumbnail shows what is on screen to anyone who has the stream id, which is in every playback URL and embed code. For paid or members-only streams keep it off; you still see the frames yourself.
• Up to a minute old. It is a preview, not a live view. For live video use the player or playback_url.
• Cost. Taking and storing frames is free. Each time one is shown it counts as delivery like video, but a frame is about 15 KB: 10,000 views are 0.15 GB, under half a cent.