What You Need to Know When Setting Up Cameras
When connecting IP cameras to a recorder or VMS, two terms come up most often — ONVIF and RTSP. They are sometimes confused, but they are very different things. ONVIF is Not “Video Stream” - It’s a standard for exchanging data and controlling IP devices. It does not transmit video or audio by itself.
Through ONVIF, the system “asks” the camera:
• what streams it supports,
• their resolution, bitrate, codec,
• which features are available (PTZ, motion detection, audio, etc.),
• and how to change settings.
ONVIF is needed for automatic camera discovery, getting a list of available streams and their parameters, and controlling the camera — for example, panning/tilting or switching profiles.
RTSP Is Where the Video Lives
After the VMS retrieves parameters via ONVIF, it gets an RTSP or HTTP link for connection.
RTSP (Real Time Streaming Protocol) is the protocol that actually transmits video and audio in real time.
Using this link, the recorder or software receives the stream and either saves it to disk or displays it live.
Why Multiple Streams Exist
Most modern cameras can output several streams (stream 1, stream 2, sometimes stream 3):
• Main stream — maximum resolution and quality, used for archive recording.
• Substream — lower resolution (e.g., 640×360), used for quick viewing in mobile apps or in multi-camera layouts without overloading the network.
• Sometimes a third stream exists, optimized for detectors or analytics, with separate parameters.
This reduces network and CPU load: there’s no need to pull 4K video if the camera preview is a tiny thumbnail.
Why Substreams Can Be Unstable
In practice, substreams sometimes fail or return errors because:
• they may not be configured properly on the camera,
• cheaper cameras may not handle simultaneous loads (main stream + two substream clients),
• different manufacturers use slightly different ONVIF profiles, and the VMS may choose the wrong stream.
Often, manually specifying the RTSP link for the substream or lowering parameters (bitrate, FPS) helps.