Video over IP
Definition
Video over IP carries pictures over Ethernet, and the design of a system depends on the balance between compression, bandwidth and latency. Uncompressed video keeps full quality with minimal latency but needs a large bandwidth: the active picture of a 1080p60 stream in 10-bit 4:2:2 amounts to about 2.5 Gbit/s, and the 3G-SDI link that carries the same signal runs at around 3 gigabits per second. SMPTE ST 2110 is the suite of standards for professional IP video; its part ST 2110-20 carries uncompressed video, and such systems are usually built on 10-gigabit or faster networks.
The guide
Compression reduces the bandwidth. JPEG XS (ISO/IEC 21122), which ST 2110-22 can carry, is visually lossless at compression ratios up to about 10:1 and adds a latency of only a few video lines. NDI High Bandwidth uses the intra-frame SpeedHQ codec, at up to about 150 Mbit/s for a 1080p60 stream. NDI HX and codecs such as H.264 and H.265 lower the bitrate further, to a few tens of Mbit/s or less, and add latency because they compress across several frames.
An oversubscribed link drops packets, and lost video packets appear as tearing, frozen frames or block artefacts. A few NDI High Bandwidth streams fit on a gigabit link, while a single uncompressed 1080p60 stream does not. Planning therefore starts from the streams: their number is multiplied by their real bitrate, a margin (headroom) is added, and the network class, 1G, 10G or 25G, is chosen to fit the total.
The rule
The number of video streams a system can carry is set by the bandwidth of its network.
Glossary terms
Sources
- SMPTE ST 2110-20 : vidéo active non compressée sur IP ; 1080p60 10 bits 4:2:2 ≈ 2,49 Gbit/s d'essence (calcul MDL Communications) · mdlcommunications.com
- SMPTE, Serial digital interface (pointeur Wikipédia) : débit 3G-SDI de 2,97 Gbit/s · en.wikipedia.org
- JPEG Committee, JPEG XS white paper (ISO/IEC 21122) : visuellement sans perte jusqu'à 10:1, latence de quelques lignes · ds.jpeg.org
- NDI, Docs and Guides, Bandwidth : NDI High Bandwidth (SpeedHQ) jusqu'à environ 150 Mbit/s en 1080p60 ; NDI HX en H.264/H.265 · docs.ndi.video
- TV Technology, Evolution of SMPTE 2110 : transport de JPEG XS en ST 2110-22 · tvtechnology.com