Mainstream: is the primary video feed. Mainstream provides the highest video quality, and is the stream the DVR / NVR uses when saving footage to the internal hard disk drive (HDD). Mainstream settings can be adjusted to increase or decrease recording resolution. These settings will impact recording file size and available recording time. Hard Disk Drive (HDD)
Sub-stream: is the secondary video feed. Sub-stream provides a lower quality video stream, and is typically used to stream video to computers, smartphones, or tablets over the Internet. This allows you to reduce streaming quality for live or remote viewing, while maintaining higher quality on the mainstream for HDD recording and storage.
When is each one used?
Mainstream: is the primary video feed mainly use for recording..
Sub-stream: is used mainly for remote viewing from computers, smartphones, or tablets over the Internet from outside the network..