A substream (or secondary stream) is a second, lower-resolution copy of a camera's video that the camera encodes alongside its full-quality "main stream". The camera publishes both at once: the main stream (say 4K at 8 Mbps) for recording and full-screen viewing, and the substream (say D1 or 720p at a few hundred kbps) for everything that does not need full detail.
Substreams exist to solve a hard limit: decoding video is expensive. A 32-tile video wall showing 32 main 4K streams would overwhelm the client's CPU/GPU and the network, dropping frames. By feeding the grid with substreams instead, the same wall stays smooth, and the main stream is fetched only when an operator expands a single camera. Server-side analytics often run on the substream too, since detection rarely needs full resolution. Many cameras now offer a third stream so recording, viewing, and analytics can each get a tailored copy.
The pitfall is leaving clients pulling main streams everywhere — the single most common cause of a laggy, frame-dropping video wall. The fix is configuration, not hardware: bind multi-view layouts and mobile clients to substreams, and reserve the main stream for recording and the expanded single view.
The handbook · 7 volumes
Fora Soft Video Engineering Handbook
A substream keeps multi-camera grids and mobile viewing fast while the main stream records at full quality, if both are configured with care. Our seven-volume handbook covers the full video stack, and for substreams start with Volume 1, which covers resolution, frame rate, bitrate control and H.264 versus HEVC settings that decide how good a low-bitrate substream looks. Written by Nikolay Sapunov, CEO at Fora Soft.
Live camera grids lagging because every tile pulls the full main stream?
We will set up a main stream and substream profile per camera type so live view stays fast and recordings keep full quality. 250+ video products shipped since 2005.
