This term is typically used to indicate a device capable of providing two different video compression methods. An example is a DVR that shows live video in M-JPEG and transmits to the remote software using MPEG-4. IP cameras often have selectable (dual stream) transmit capability. This may sometimes refer to two streams of the same compression method with different parameter settings.
Dual Stream refers to the ability of a camera to output two simultaneous video streams with different resolutions or qualities. One stream may be high-res for recording, the other low-res for remote viewing ā optimizing bandwidth use.