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Guide · AirPlay

Apple TV lip sync over AirPlay: measure and fix the delay with your iPhone

When an Apple TV sends its sound over AirPlay, the picture has to wait for the audio; the Apple TV delays the picture by the latency the receiver announces, and if the real delay is different, voices land before or after the lips. The audiolaz corrector (an AirPlay receiver on a Mac or Linux machine, in test) measures the real delay: the audiolaz Synchro app on the Apple TV plays a test pattern, the iPhone listens at your seat and measures the gap between picture and sound, and the corrector is set to match.

Updated by Alexandre Besson, who makes audiolaz. audiolaz Room is in beta.

Why

Several small delays add up.

  • The AirPlay buffer. AirPlay plays from a buffer so the network does not cause dropouts; the receiver announces its latency and the Apple TV is meant to hold the picture back by as much.
  • Processing. A convolution filter, upsampling, a DAC’s own filters and buffers all add time the announced figure may not include.
  • The TV. The picture itself may be delayed by the TV’s processing, which no audio device sees.

Each is small; together they can be enough to see.

Measure

A test pattern, an iPhone, a number.

  1. On the Apple TV, open audiolaz Synchro and choose the pattern: Stereo or 5.1. It needs no network and no account.
  2. Send the Apple TV’s sound by AirPlay to the audiolaz corrector.
  3. In audiolaz Room, on the iPhone, open My players › Measure the sync, tap « The pattern is playing » and hold the phone at your seat, facing the screen; it measures the gap between picture and sound.
  4. The corrector takes the result: its AirPlay input is set so the sound lands with the picture.

Measure again if you change what sits between the corrector and your ears: another DAC, another output, upsampling switched on.

The corrector

AirPlay in, your DAC out.

The audiolaz corrector runs on a Mac or on Linux (DietPi, Raspberry Pi OS, a Linux Roon Server…). Inputs: AirPlay (from an Apple TV, an iPhone, an iPad or a Mac), Roon, Spotify Connect, UPnP. Output: a USB DAC, a Diretta target or a network streamer. It plays the room’s filter too, so the Apple TV’s sound is corrected like your music. It also receives 5.1 and 7.1 and mixes them into stereo, the centre channel in the centre; as an option, “Dialogue” makes voices clearer. It is part of Room Plus and is in test (on the home page).

Without audiolaz

Wireless Audio Sync, and its limits.

tvOS has its own calibration: Wireless Audio Sync, in the Apple TV’s Video and Audio settings, measures the delay with an iPhone held near the TV. It is worth trying first, it is free and built in. It measures through the iPhone’s microphone near the screen, not necessarily what happens after a convolution filter and a DAC at your seat; when the result still looks off, a measurement made through the whole chain is the next step.

Questions

Short answers.

  • Stereo and 5.1?

    The audiolaz Synchro app has a Stereo pattern and a 5.1 pattern.

  • Does it work with a HomePod?

    No: the measurement sets the audiolaz corrector; a HomePod is its own AirPlay receiver.

  • Do I measure again after changing DAC?

    Yes: a new DAC or output can change the delay.

  • Does Roon have the same problem?

    Roon plays music, without a picture to follow; the delay does not matter there.

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