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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)?

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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.

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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; it’s a red flag when an Amazon title is peppered with every potential search keyword like there.

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.

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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
    Commented Feb 28, 2023 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
    Commented Feb 28, 2023 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
    Commented Feb 28, 2023 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
    Commented Mar 1, 2023 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
    Commented Mar 1, 2023 at 14:58

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