Secu­re Relia­ble Trans­port (SRT) and Net­work Device Inter­face (NDI) stand for AV-over-IP solu­ti­ons that enable high-qua­li­ty video trans­mis­si­on with low laten­cy, but still ser­ve dif­fe­rent applications. 

SRT has an inte­gra­ted two-way return chan­nel that trans­mits essen­ti­al per­for­mance infor­ma­ti­on during strea­ming. This enables the pro­to­col to detect and rec­ti­fy pro­blems. To use SRT, the enco­der and deco­der must be SRT-com­pa­ti­ble. When using SRT, band­widths of 2–8 Mbit/s are suf­fi­ci­ent to stream in high quality.

Advan­ta­ges of using SRT

  • relia­bly deli­vers vide­os with low laten­cy and high quality
  • enables simp­le and cost-effec­ti­ve deploy­ment of remo­te locations
  • Easi­ly over­co­mes fire­walls bet­ween source and destination
  • High secu­ri­ty (up to 256-bit AES encryption)

NDI stands for a soft­ware stan­dard with which vide­os can be trans­mit­ted and recei­ved in high qua­li­ty and with low laten­cy via a local area net­work (LAN). This means that seve­ral audio and video devices in the net­work can be acces­sed via a sin­gle LAN connection.

The main pre­re­qui­si­te for NDI strea­ming is that the sen­ding (NDI-capa­ble) and recei­ving device are in the same net­work. For exam­p­le, the video image from an NDI-capa­ble PTZ came­ra can be sent and recei­ved via a com­pa­ny-wide net­work. At the same time, the came­ra can be con­trol­led via the net­work. Other devices may requi­re addi­tio­nal setup.

NDI tech­no­lo­gy uses a spe­cial codec and a trans­port method to achie­ve vir­tual­ly los­sless image qua­li­ty wit­hout laten­cy. Howe­ver, this means that NDI requi­res a very high net­work band­width. A sin­gle 1080p NDI stream at 30 fps requi­res a band­width of at least 125 Mbps.

Until recent­ly, the­se high band­width requi­re­ments meant that NDI-based video work­flows were only plau­si­ble over sta­ble local net­works. With the release of NDI 5, this limit has now been excee­ded. By using the NDI bridge tool, two remo­te NDI net­works can be con­nec­ted to each other. Live audio and video can be con­tri­bu­ted via a URL using the NDI remo­te tool.

Advan­ta­ges of using NDI

  • Almost los­sless qua­li­ty wit­hout latency
  • All video sources are easi­ly acces­si­ble from any­whe­re in the network
  • offers cost-effec­ti­ve video pro­duc­tion via LAN