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I have a VP2768A monitor (provided by my employer), and I bought a lightning to HDMI cable yesterday because I wanted to project my iPhone 12 Pro to a larger monitor for certain activities (e.g. gaming). However, I noticed that there's a delay. It's not too bad (maybe around 100ms or so), but it's definitely not ideal for certain activities.

This is the cable that I purchased: RAVIAD Apple MFi Certified Lightning to HDMI Digital Cable

I don’t know if it's possible to reduce or eliminate the delay. Should I try switching the cable or is the latency more associated with the iPhone/monitor (which I can't replace)?

Allan
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dzdang
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2 Answers2

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Should I try switching the cable or is the latency more associated with the iPhone/monitor (which I can't replace)?

You could try switching out the cable, but you’re not likely to see much improvement. Your device itself isn’t the problem here, it’s the conversion from USB to a digital video signal that’s the culprit.

It’s technically a USB to HDMI adapter

The Lightning port does not supply a native video signal; just four data lines. As such, it only supports a small number of signals: USB, charging, and audio (via a DAC). This means that the video must be “created” to connect to your display/TV.

Basically, there is a typical USB to HDMI (or VGA for analog) adapter embedded in the cable; it’s actually just the chip. That chip is just enclosed in an “all-in-one” cable that goes from the Lightning connector to the HDMI connector.

Creating video takes time

This video signal creation means there is an inherent latency no matter what you do. It takes time to create that signal and it will be nowhere as fast as the embedded GPU in your iPhone.

Get a better cable…

You could potentially reduce the latency with a higher quality cable from a reputable cable manufacturer(I am partial to Anker, CableMatters, Belkin) or get the Apple Lightning to Digital AV adapter. (IMO) The cable that you linked is from an unknown brand (likely Chineseium); it’s a red flag when they pepper their Amazon title with every potential keyword like they did.

TL;DR

Bottom line, try a better quality cable to reduce the latency, but in this case, you cannot eliminate it. It’s also important to remember, this feature was meant for mirroring your iPhone display for convenience, not to be an external display in which performance is a factor.

Allan
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  • Got it, thanks. My 100 ms in the OP was just a rough estimate, but I was wondering if you have any insight into what latency can be expected with more reputable cables? – dzdang Feb 28 '23 at 18:12
  • also, my monitor does have a USB-C input, but I don't think I've seen a lightning to USB-C cable that's meant for external displays. seems all the existing tables are solely for charging – dzdang Feb 28 '23 at 18:13
  • I don’t know of any testing done to judge the latency of cables. As far as the USB-C monitor goes, the device would have to support USB-C Alt Display Mode which the iPhone doesn’t – Allan Feb 28 '23 at 18:21
  • I was trying to find cables under the brands you mentioned but it doesn't seem they make lightning to HDMI cables? – dzdang Mar 01 '23 at 14:50
  • I would get the Apple Lightning to Digital AV adapter and just use a generic but quality HDMI cable. This way you can be certain that you’re getting a chip that Apple approves of. – Allan Mar 01 '23 at 14:58
  • Revisiting this as I recently purchased an ipad pro 6th gen (the latest one). I used the USB-C to HDMI connector, and it seems there's no latency compared to the iphone 12 pro previously. I wonder if this is because there is no lightning port involved with the ipad or better hardware? – dzdang Mar 17 '23 at 14:35
  • USB3 Gen 2 is much faster (2x) than Lightning pkus you have a faster CPU. – Allan Mar 17 '23 at 15:21
  • USB3 Gen 2 and the faster CPU actually have nothing at all to do with that. The reason for it having no noticable latency is that the iPad Pro 6th Gen has a Thunderbolt/USB4 port that natively supports DisplayPort over alt-mode. So you get the DisplayPort signal directly from the iPad's "GPU". – jksoegaard Jul 28 '23 at 22:19
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The latency comes from the cable - which is actually not just a cable, but rather active electronics as described in the other answer. This also means that the latency depends on the quality of that electronics.

The Apple Lightning to Digital AV Adapter has a latency that is ~70 ms. If your adapter really has a 100 ms latency, then you could reduce that latency by switching to Apple's adapter.

If you do not know the latency, an easy way to get a good estimation of the latency is to connect your phone to the monitor using your cable, start up the Watch app and start a stop watch running.

Now with a second iPhone, use the Camera app to record a slow motion video (which can be set to 240 fps on a modern iPhone), and film both the iPhone's display and the monitor at the same time.

Afterwards you can play back the video, pause it, and compare the timestamps show on the iPhone and the monitor. The difference is the latency.

jksoegaard
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