Main-stream and sub-stream concept was first developed by Hikvision. This technology has been used in Hikvision DVR to offer smooth video streaming for remote monitoring. Now it is widely used in DVR, NVR, IP camera across different manufacturers. This technology also called Dual-stream technology, it adopts one channel main-stream to deliver high definition video for local HD video recording/storage, such as 5 megapixel, 3 megapixel, 2 megapixel (1080p), 1.3 megapixel (720p), meanwhile one channel sub-stream to deliver low or standard definition video over Internet for remotely surveillance (e.g. viewing cameras on a smartphone). Dual-stream technology enabled video surveillance products deliver high definition video for local video storage, meanwhile overcomes 3G/ADSL network bandwidth limitation to deliver smooth low/standard definition video.
Main-stream: stream resolution is higher than sub-stream, for local video streaming, output high definition video to display on the local monitor, also record HD video on your local network network video recorder (NVR). Currently, the main-stream resolution are 2560x1920 (5 megapixel), 2048x1536 (3 megapixel) 1920x1080 (1080p) and 1280x720 (720p). Additionally, main-stream delivers real-time (30fps or even high frame rate 60fps) HD video stream, this can ensure local recording footage offers detailed information without missing anything important.
Sub-stream: offering low/standard definition video primarily for lower bandwidth situations, the sub-stream resolution are QCIF, CIF, 2CIF, DCIF, 4CIF (D1). The majority video surveillance products can automatically choose appropriate sub-stream resolution to match your smartphone's display resolution. Furthermore, sub-stream may not transmit real time video, but transmit key frames and sub-frames to deliver video. This also can decrease the network bandwidth burden, which in turn to achieve smooth video monitoring in low bandwidth situations.
In addition to dual-stream technology, some IP cameras support triple stream technology. Triple stream means the IP camera can simultaneously output three different video streams, each of video streams can be configured with different resolution, frame rate, bitrate and codec type. Triple streams give much more flexibility to users by allowing different data stream to be send simultaneously, and each for independent purposes. For example, Hikvision smart IP cameras support triple streams: