Q. What causes lip-sync issues?

Modern video processing systems in TV’s and Projectors take a finite amount of time to process the incoming video data before displaying it.  This processing time can vary depending on the input port of the device, the resolution of the supplied video, and the settings of the display itself.  By comparison, the Audio more or less passes straight through the processing with a tiny delay in comparison.  As video resolution and colour depth increase with HD, 4K, UHD, and HDR, the processing overhead is only set to increase and worsen the problems.

If you have a single TV and use the inbuilt speakers, then everything should be in sync as the TV will delay the audio automatically to correct for the video processing delay.   If, however, at any point, the audio and video are separated and processed by different equipment, problems can occur.  This is why AV amplifiers have an audio delay setting, to permit the user to delay the audio by the amount required to bring things back into sync.  You will also see some TV’s have an Audio delay feature connecting external speakers or soundbars.  There are also in-line audio delay units available from various suppliers to introduce an audio delay to bring things back into sync.

In Post Production where the audio and video are separate elements on a timeline, there is the possibility for one to slip with reference to the other.  Some codecs, hardware, and toolsets can also introduce an error, so checking the final rendered output becomes necessary to ensure things have remained in sync.  As a minimum general system checks should be made when any component, hardware or software, is altered or updated.

This website has some great details on the causes of AV latency.

Q. How ‘bad’ does it need to be for someone to notice?

People can generally perceive a lip-sync error when the audio leads the video by 15ms - 35ms.  Oddly if the audio lags the video, this goes up to around 80ms, probably because it’s more natural to have images arrive before the sound. For example, speaking to someone across a room means you see them talking before you hear them.

Trying to adjust or check any system manually is always prone to error, as it relies on the person's subjective view of doing the testing. In addition, everyone will perceive the size of the error differently, meaning that any correction made will not be a true reflection of the system performance.  Different sources may also have differing error levels, so the sum of the errors can lead to things looking wrong.

The ideal is to have the base system setup as accurately as possible, so if a source, such as a particular Blu-Ray film or streaming service, has a slight error, it may well go unnoticed.

Q. Hang on, HDMI 1.3+ supports auto-lip sync, so why do I need to do anything?

There is a feature within HDMI 1.3 and above where the display can send an audio delay figure back to its source.  This is a generic delay, possibly one of two, depending on whether the source is an interlaced signal or not.  This is an average delay coded by the display manufacturer and only covers the average processing delay of the display unit itself.  There is also a reliance that the source feeding the display actually knows what to do with this delay when it receives it.

In real terms, it’s a start, but it doesn’t consider the entire system, just the display.  In addition, there have been reported issues with the feature if the HDMI Consumer Electronics Control (CEC) is also used.  You may see this described as Samsung Anynet+, SimpLink from LG, Philips Easylink, BRAVIA Link and BRAVIA Sync from Sony etc.

Q. What type of display does Sync-One2 work with?

Sync-One2 will work with any display, whether a TV (LED, Plasma) or projection (front or rear) and at any resolution.  When using a front projector in a bright environment, it may be necessary to put Sync-One2 into the projector beam.  Sync-One2 is the only real way to ensure the video is in sync with the audio when using a projector.

Q. You mention self-calibration; what does that mean?

When you first turn on Sync-One2 or go back into measurement mode from the menus, it will calibrate.  This only takes a few seconds and is used to make things easier.  The unit determines the ambient light level, which and can also normally remove any flicker from lighting from interfering with the readings.  On the audio side, the gain of the microphone is adjusted to reduce the ambient noise to a level that does not interfere with the readings.  This is why it’s important to have the unit in the measurement position when turning on or going back into measurement mode.

In addition to the calibration, both the light and audio sensors have adjustable trigger levels to alter their sensitivity. They are the most sensitive by default but can be turned down as needed using the respective option within the menus if the local environment requires it.

All these details are in the full user manual, which you can download from the Support page.

Q. By accurate, how accurate do you mean?

As an indication, internally, Sync-One2 is very accurate.  The smallest error between the flash and a beep detectable is 0.05 milliseconds, and all internal calculations are processed internally at that resolution.   The display is rounded to the nearest millisecond or 1/100th of a frame.

Q. I think my Sync-One2 isn’t detecting signals as it should; what could be wrong?

Most such issues are not having Sync-One2 in the measurement position during calibration or having a test file playing past the lead-in time.  Detection will only happen if the beep and flash are louder and brighter than the levels detected during the calibration.  So if Sync-One2 calibrates when a test is playing, it will helpfully calibrate out the flash and beep and not trigger.

If you have a space with a high reverberation time, you can increase the mask time to give the sound time to decay before Sync-One2 re-arms for the next measurement.

Short version

Yes, there are, but they many fundamental problems.

Long version...

Indeed there are apps available. However, they all suffer from many fundamental limitations; the use of a video camera for the ‘flash’ detection, reliance on an underlying operating system, and manual snapshot detection.

Let us talk about each of these areas;

“Flash” detection

In terms of the video camera, by definition, cameras operate on whole frames.  So the minimum time period between any two readings is based on the physical frame rate that the camera can sustain during the measurement period.  This varies between 30fps to 240fps, depending on the hardware.  This can mean the potential error windows, based on frame rate alone, will be a minimum of around 64ms to 4ms.

Underlying Operation System

The apps do not directly talk to the hardware, the underlying OS has to process the audio and video and pass it to the app.  The OS is also doing all the other things it needs to do, such as updating your e-mail or handshaking with a cell tower.  All of these things can introduce non-deterministic errors to account for.  These delays could change with an OS update, what other Apps are running on the device, or potentially a minor change to the hardware itself.  Generally, some kind of average correction factor (read fudge factor) needs to be worked out for each device model and OS version combination for you to enter into the App.  This also introduces inaccuracies, as this is an average correction, not a deterministic correction, but one worked out at a single point in time and published by the authors.  (You did remember to check if this has changed since the last time you set it, too, especially if there has been an OS or App update?)

For example, for the Apple devices, you have 14 types of phone (4, 4S, 5C, 5S, SE, 6, 6 Plus, 6S,  6S Plus, 7, and 7 Plus, 8, 8 Plus, and X), then throw in iPads and iPods too.  Each will have its own specific inaccuracies to be accounted for.  Add in the OS version into the mix, too, and things get a bit more complex.  Since iOS 7 was released, 57 versions of iOS have been published (iOS 7 had 10 versions, iOS 8 had 11 versions, and iOS 9 had 12, iOS 10 had 11, and iOS 11 is up to 13).  Any of these updates can cause an inaccuracy needing an approximate correction to be determined and entered, which could also be device-independent. For example, an iOS update from 7 to 8 on an iPhone 5S has been seen to alter readings by ~20ms, or around 0.5 frames. For newer Apple hardware, there are warnings over problems too, causing variances or ~30 ms (that's over 1 frame!) depending on which version of iPhone you have.

One reason the supported hardware lists are restricted is the requirement to test all these combinations, which is an ever-increasing task as updates and devices come along.

Manually assisted snapshot detection

Lastly, there is the issue that you have to do some work to get your measurement. You cannot just read it off the screen in real-time like you can on a Sync-One2.  To use the Apps, you need to film a few seconds of video, then stop and manually slide the audio along with match the video frame showing the flash (potentially one of many) to give the approximate error.  This is the error for a single beep flash, not the system as a whole.

If the system under test isn’t perfectly stable, then the error provided will not be a fair representation of the system under test, just the error of the single frame of the video when you took the film.  To really measure a system, several readings are needed to average out the fluctuations in the system under test, also using a test with a variable gap between the beep/flash tests.  That simply isn’t possible with an App.

Sync-One2 uses an analogue light sensor, so it has no minimum measurement interval.  The microprocessor in a Sync-One2 is doing nothing but trying to do the job at hand, so nothing else can get in the way of making an accurate measurement.

Sync-One2 also shows you the error in real-time, in milliseconds, and frames if required.  You can also show a running average in real-time (in frames or milliseconds), so it’s easy to watch for drift over long periods (around six hours was the longest we know about, by a company testing an international Video Conference link). Finally, statistics of the most recent 60 readings show you how stable a system is and help see what is really going on.

To sum up, you can use an App if you want.  However, if you want to be accurate, have a real indication of how any system is actually performing, not spend the time doing the measurements manually, forgetting to look up and enter correction factors, and so doing it all again, simply do what the professionals do and use a Sync-One2.

Q. Why a V2?

The original Sync-One2 has remained largely unchanged since 2014. However, since launch, several requests have been received for additional features, which customised bespoke versions for various customers have accommodated.  These have required both firmware and hardware modifications.

Technology has also moved along since 2014, so we decided to bring Sync-One2 up to date and roll in previous custom enhancements into a new version.  This gives everyone the benefit of the added features and creates something more flexible for those who need them.

Internally Sync-One2 is based on new hardware, requiring the firmware to be ported to a new processor.  This has also enabled improvements that were not possible before and the ability to have new features added with a firmware update not previously possible.

Q. What does v2 do that the original didn't?

Well, where to start.

The most obvious difference is the addition of two additional holes in the case on the left-hand side.  These are for a 3.5mm audio input jack and a USB Mini-B connector.  The audio jack is a normal stereo input (downmixed to mono internally) that enables v2 to be directly connected to a headphone or line-output interface to take an audio feed rather than use the internal microphone.  The switchover is automatic but may also be overridden via a menu option if needed.

The USB Mini-B will appear as a standard Serial port on Windows, Mac, or Linux computers. Without any additional effort, v2 will log all readings taken in Measurement mode to the port, so it becomes easy to grab readings.  Via this port, there is also now an API interface to v2 to remote control the unit.  This may be to use Sync-One2 v2 as part of a bench calibration or inspection process or to easily obtain more detailed statistics to generate a certification report for an installation you can give to a client to show them the data.

You can also add some custom startup splash text to the display (via the API), such as your name and number, should the unit get mislaid. We can also program, at the time of order, a permanent custom message.  This could be a company ownership message, or branding, in a way that a user cannot remove, like a label or asset tag.

The USB Mini-B port also permits the end-user to upgrade the firmware when new features come along or require some new function or feature not currently there.

There are also new features, such as adjustable Mask Time for spaces with long reverberation times.  Enhanced sensitivity of the light and audio detection sensors.  Brighter display, which is also now blue rather than white.

Q. What is a feature or support code?

A Support Code is an easy way to pass information about any given unit back to us for support.  The code contains unit-specific information such as serial number, firmware revision, and installed or activated features.  It may also be requested to verify ownership for specific requests for complex test files.

A feature code is used to perform a specific action specific to a Sync-One2 v2, enabling an enhanced feature.

Q. What about support for my original version?

There is still support for the original version, and the warranties remain valid. In addition, should a unit require service, we have spares if there is a problem or a unit suffers physical damage.

I press the On button, and nothing happens.

For Sync-One2 v2, you must hold down the On button for a few seconds to turn the unit on.  Why, you may ask? Well, Sync-One2 does turn on when you press the button, but it is very busy performing internal verification checks on the firmware.  Once these are complete, the display will wake up, and everything is ready to go.

What does "Waiting for PC" mean on the display?

During power-up, Sync-One2 verifies the internal firmware is intact and has not been tampered with. If this fails for any reason, then this message is displayed.  It means the unit is awaiting firmware to be uploaded, which can be found on the support pages.

Normally this error only happens if a firmware upgrade has been interrupted, in which case try again. However, if an attempt has been made to tinker with the firmware, please stop it and reload the unaltered firmware.

If the error appears at first power on, and then Sync-One2 starts up as normal after around 30 seconds, buy a lottery ticket.  The probability of a Sync-One2 doing this is 1 in 4,294,967,296.  If this keeps happening on your Sync-One2, please get in touch, it is easily fixable, but we will need the unit back to work some magic.

Please note that some playback solutions may show an audio latency of 2112 samples because of the nature of AAC encoding.  This is equal to an audio delay of 44ms for 48 kHz audio (this translates to an audio stream that can be late by around 1 frame in 24/25 fps and around 2 frames in 50/60fps ).  While some decoders compensate for this latency, not all solutions do. Therefore, it is recommended to use the PCM files to measure the latency of your system with the best possible accuracy.

To check your system's audio/video synchronization, make sure to check with either PCM or AAC files depending on the audio format you use primarily on the system to calibrate.

You can read more about this delay caused by AAC encodings here: https://developer.apple.com/library/archive/documentation/QuickTime/QTFF/QTFFAppenG/QTFFAppenG.html

Credit to DXOMARK for some in-depth technical analysis to identify this issue.