Channel previews¶

The channel list in an operator's app, the EPG and a monitoring wall all need pictures: what is on air right now. That is what channel previews are for — the streamer regularly renders a JPEG frame and serves it at a stable address. Configured in the Thumbnails block on the Process tab.

Configure a preview¶

Press + Add thumbnail and pick the Source:

• Stream keyframe — the streamer renders JPEGs from the channel's keyframes. Fields: Track (the video track, usually v1), Width and Height (one is enough — the other follows the proportions; the default width is 320), Every — how often, in GOPs (gop — every one, 2gop — every other).
• HTTP fetch — the streamer does not render at all: it periodically fetches a ready-made picture from the HTTP fetch URL — handy with IP cameras that serve a snapshot.

The Store thumbnails in DVR switch additionally writes the thumbnails into the archive — along with the channel's recording you get its visual filmstrip.

A channel can carry up to ten preview tracks — a small one for the list and a bigger one for the channel card, say.

Fetch the picture¶

The channel's fresh frame is served at:

/streaming/live-preview-jpeg/<channel-name>

The answer is a plain JPEG; a client interface simply re-requests it at whatever cadence it needs:

While the channel has no previews configured, the address answers 404 — thumbnails do not render by themselves, they are work you have to turn on.

If there is no picture¶

• 404. Previews are not configured, the channel is off air, or the first keyframe has not arrived yet — with Every: 2gop and a long GOP the first frame can take tens of seconds.
• There is a picture but it froze. The preview source is an HTTP fetch and the camera serves a cached snapshot; check the camera's URL directly.
• The track is not found. The Track field must name an existing video track of the channel — look its id up in the source health card (usually v1).