Cable delay in lines and pixels, the advance to set on your sync generator, and the timing figures for every broadcast format. Everything runs in your browser.
Pick the format you are timing. Everything below is derived from the total line count and the pixel clock, not from the active picture.
Total lines and total samples per line include blanking, which is what the pixel clock counts. Interlaced formats are listed by frame rate: 1080i/50 is 25 frames per second, so a line lasts the same time as in 1080p/25.
Signal travels slower than light in a cable. How much slower is the velocity of propagation, and it is printed on every datasheet.
Velocity of propagation figures are from published cable datasheets and are typical, not guaranteed: check the one you are actually pulling. Fibre is computed from the group index, so it is slower than a foam coax of the same length.
A camera fed by a long reference run answers late at the switcher, by the reference cable delay plus the return video cable delay. Advance the sync output feeding that device by the total.
Both runs use the cable type selected in section 2. Processing delay is device-specific and is never in the cable: take it from the manufacturer or measure it. This calculation gives you a starting point to type in, not a substitute for looking at a waveform monitor.
Sync generators take offsets in lines and pixels, datasheets quote microseconds and metres. Convert in either direction, in the format selected above.
Edit the microsecond field to get lines and pixels, or edit lines and pixels to get the time. The last field you touch drives the other.
Many plants still distribute 625/50 or 525/59.94 black burst as the house reference while the video is HD. The offset you type into the generator is counted in the reference format's lines, not the video format's.
A line of 625/50 black burst lasts 64 µs, a line of 1080i/50 tri-level lasts 35.5556 µs. The same delay is therefore a different number of lines depending on which one your generator is counting. Getting this backwards is the classic way to end up a line and a half out.
Built by Elettronica Mangione, Rome — broadcast synchronisation since 1984. Line and pixel figures are derived from the published SMPTE and ITU-R total line counts and pixel clocks. This tool computes; it does not certify. Confirm against a waveform monitor before you sign off a facility.
Genlock — short for generator locking — is how every video source in a facility is made to start its frames at the same instant. A central sync generator sends a reference signal, historically black burst and in high definition tri-level sync, to every camera, server and graphics machine. Each one aligns its output to that reference. Without it, cutting between two sources tears the picture, because the switcher is asked to change source in the middle of a frame.
A signal does not arrive the moment it leaves. In a foam-dielectric coax it travels at about 83 per cent of the speed of light, so roughly four nanoseconds per metre. One hundred metres of cable delays the reference by about 402 ns.
That sounds negligible until you count it in pixels. At 1080i/50 a pixel lasts 13.468 ns, so those 402 ns are almost thirty pixels — a visible horizontal shift on a waveform monitor and enough for a switcher to reject the source as out of time. In UHD, where a pixel lasts 1.68 ns, the same cable is nearly 240 pixels.
A whole line is a much longer distance than people expect: at 1080i/50 one line lasts 35.56 µs, which is about 8.8 km of coax. So in a normal building you are almost always working in pixels, not lines. The tool above shows both.
The delay is paid twice. The reference travels out to the camera, and the camera's video travels back to the switcher. Both runs add up, and the sum is what the source is late by at the point where timing is judged.
So you advance the sync output feeding that device by the total. A camera on an 80 m reference run answering over a 120 m video run is 200 m of cable late, about 804 ns, which at 1080i/50 is 59 pixels. Advance its reference by 59 pixels and it lands on time.
Any processing delay inside the device is on top of that and is not in the cable. It has to come from the manufacturer or from a measurement — no calculator can guess it.
Black burst is a composite signal with a black picture, used as a reference since the analogue era, and still distributed in a great many facilities. Tri-level sync uses three voltage levels and a steeper transition, which is why it is preferred for high definition: the point at which a receiver decides the sync has arrived is less ambiguous, so the timing jitter is lower.
Here is the trap. Your sync generator counts its offset in lines of the reference format, not of the video you are timing. A line of 625/50 black burst lasts 64 µs. A line of 1080i/50 tri-level lasts 35.5556 µs. The same delay is a completely different number of lines depending on which one the generator is counting, and typing the HD number into a machine referenced to black burst puts you most of a line out. Section 5 above shows the same offset expressed every way, so you can see which number belongs in your generator.
All the arithmetic here uses total lines and total samples per line, blanking included, because that is what the pixel clock counts. 1080-line video is 1125 total lines; 720p is 750; 625/50 is 625 and 525/59.94 is 525. Multiply the total samples per line by the total lines and by the frame rate and you get the published pixel clock exactly: 13.5 MHz for standard definition, 74.25 MHz for HD, 148.5 MHz for 1080p/50 and 594 MHz for UHD at 50 Hz.
Using active lines instead — 1080 rather than 1125 — is the other common way to get a timing calculation wrong by several per cent.
Most facilities are now hybrid. Part of the plant is still SDI, referenced to black burst or tri-level. Part is SMPTE ST 2110 over IP, referenced to PTP. The two timelines have to describe the same instant, or a source that is in time on one side is out of time on the other.
That is the job of a grandmaster that speaks both: disciplined by GNSS, serving PTP under SMPTE ST 2059-2 to the IP side, and driving the black burst and tri-level distribution on the legacy side, from one clock. If you are timing a facility with this calculator, that is the equipment underneath it, and it is what we build.
These tools are free because we build the equipment that does the same job in a control room, twenty-four hours a day, without a browser tab open.
Elettronica Mangione has been designing broadcast synchronisation systems in Rome since 1984, with over 1,000 installations in 15 countries. Talk to a timing engineer.
About four nanoseconds per metre for a foam-dielectric coax with a velocity of propagation of 83 per cent, such as Belden 1694A. A solid polyethylene cable at 66 per cent is slower, about 5.05 ns per metre. Fibre is around 4.9 ns per metre, slightly slower than good coax, because the figure comes from the group index of the glass rather than from a dielectric.
At 1080i/50, where a pixel lasts 13.468 ns, 100 metres of 83 per cent coax is about 30 pixels. At 2160p/50 a pixel lasts 1.68 ns, so the same cable is close to 240 pixels. The number of pixels depends entirely on the pixel clock of the format you are timing.
Advance it. The device is answering late by the time the signal spends in the cable, so you send its reference early by the same amount to bring the return into time at the switcher.
Both. The reference travels out and the video travels back, and timing is judged where the video arrives. A camera on 80 m out and 120 m back is 200 m of cable late.
Black burst is a composite signal carrying a black picture, inherited from analogue and still widely distributed. Tri-level sync uses three voltage levels with a steeper zero crossing, which makes the moment of arrival less ambiguous and lowers timing jitter, so it is preferred for high definition.
Because a sync generator works by counting its own pixel clock. Its offset is a number of clock periods, and it displays them as lines plus pixels. The catch is that they are lines of the reference format it is generating, which may not be the format of the video you are timing.
Yes. 1080 is the active picture; 1125 is the total including blanking, and the pixel clock counts the total. Timing arithmetic done on 1080 rather than 1125 comes out several per cent wrong.
In a hybrid plant, yes. The SDI side still needs black burst or tri-level while the IP side is referenced to PTP, and both have to describe the same instant. That is why grandmasters for broadcast generate the legacy reference as well as PTP.
Yes, with no registration. Everything is computed in your browser and nothing you type is sent anywhere.