Can a very thin and long HDMI cable add latency?

[RoyZ7]

Hi friends,

I have a question, I have a Canon SL3 (250D) DSLR camera and I have some delay (400ms-500ms) previewing the video coming out of it using its HDMI output and external displays. eventually I'd like to capture the video coming out of it using a capture card in real time, so I aim for the least amount of delay I could get.

Among other things I'm ruling out (like camera settings), I suspected the delay might be caused by the HDMI cable (HDMI to HDMI mini) which is very very thin and about 6 feet long, it only say "high speed HDMI" on it. I got two different looking/no-brand "HDMI to HDMI mini" cables but they are the same thickness and length and perform the same.

I have read that an HDMI cable is suppose to work or not. like a 0 or 1 result.

So my question is really, if the amount of information is very big like very high bit-rate, uncompressed data as this camera's HDMI output can output:


Can cables like those "slow the data down" and cause delay? or if it works it already means the cable can't add a delay by itself?

I've learned that HDMI 2.1 is the latest version of the cable which supports up to 48Gbit/s, my next step would probably be to by an HDMI to HDMI mini adapter and an HDMI 2.1 cable like that and try, but would love to get an educated answer.

Thank you very much,

Roy.

[Cornucopia]

Not in the way you are thinking...

ALL cable has delay, but it is miniscule. It has an effect when transmitting baseband ANALOG video (hence the old engineering need to "time" the component wires), but with serial or parallel digital video streams - which already incorporate muxing/demuxing timing alignment buffers along w error correction - alignment is not an issue. And overall delay is ESPECIALLY tiny at only 6 feet.

The difference between high-speed and non-high-speed cabling for HDMI has to do with isolation from interference (and its accompanying errors) AT those high speeds. IOW, if you are REALLY lucky, you could use a non-high-speed cable and run the signal at high speeds through it without issue. But I wouldn't get my hopes up. Those are rated for what they would normally be able to support, and are usually quite accurate.

(assuming 30fps here)
Your 400ms+ delay is at least a 12 frame (.4sec) delay! That's quite a lot, and is likely due to the previewing output electronics in the cam (the source), not the cable and not the display, and nothing you can change. Shame.

Scott

[jagabo]

Cable propagation delays are on the order of single digit nanoseconds per meter of cable.

The reason for your ~500 ms delays have to do with buffering in the camera and in the display, not the cable.

[DB83]

This reply will probably not help you much but.......


A 6 foot cable is NOT long. Double, triple or more than that is long.


A 2.1 cable is not gonna help you for 2K or even 4K (AFAIK the limit for this camera) transmission. That new standard is designed to 8K and beyond.


And re-read that wiki article which you possibly got your info from. Only part of that speed is used for actual video.


'Delay' is not necessarily a consequence of cable but the recording. And more so if you do not see any sound-sync issue since the playback device has already allowed for that.


And do not get me started on a DSLR being used for video. Use a bespoke video camera for that and leave DSLR for pictures.

[KarMa]

An uninterupted line of fiber going from New York to LA would be about 20ms via fiber, one way. Electrons through copper are faster. Your HDMI is going to fail to work due to being too long, before you ever notice the latency.

[RoyZ7]

Thank you very much everyone. I've learned something

I've also discovered I had an issue that the video stopped showing on my PC, "streaming" from my camera to the capture card after about 2 minutes,
so I was pretty sure it's because the cable is not good enough.

So I have bought the better HDMI 2.1 cable and an HDMI to HDMI mini adapter to test it out and it doesn't now it doesn't stop playing.

as you all said, I don't see any improvement with the latency.

I have ran a few tests and I've measured latency values and discovered some interesting things:

Shooting and streaming to the computer in 4K 24fps: The camera's display is 180ms late and the PC display- after being captured by the capture card, is 230ms late. that means the capture card adds only 50ms and most of the delay is by the camera.

But what I care about more is 1080P 60fps, and with that setting, the camera's display and the capture card are 100% synced. the capture card doesn't add any additional delay. but they are both 160ms late after the source.

I was trying to change every possible setting in the camera as for the video settings to see if it effects the speed that the camera shoots and outputs the video, but nothing has changed it.

I'll try to write Canon about it, maybe I'll get lucky and they'll have a tip for me or they might do something about it in the next firmware update if they can. but on the other hand I bet they would already do it if they could right?

I know 160ms doesn't sound like a lot but if I look away from the camera and then look back while previewing that on the computer's screen, It's just in time to see my eyes move.
and the lips are not synced and I'm about to record many hours of video for a project I'm starting, so I just wished/thought it will all be 0 latency.

Thanks again everyone.

Roy.

[Cornucopia]

It will never be 0. But it isn't unreasonable to assume <50-60ms. Basically, <2 frames. In video/ENG/digcinema cams.
Doubt you will see that in consumer dslrs. Maybe in mirrorless, maybe not.

That's one more thing that separates devices based around video vs those based around still photo, even though there is overlap.

Scott