AirPlay screen mirroring sound lag using two Apple TVs

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Level 1

8 points

AirPlay screen mirroring sound lag using two Apple TVs

I want to connect my new 5th Gen. ATV via HDMI to my projector (Epson EH-TV5350) and send its sound wirelessly to my old 3rd Gen. ATV connected to (old, non-bluetooth) speakers. But:

When AirPlay mirroring my MacBook Pro or iPhone screen to the 5th Gen ATV, I do get a good picture with the projector and the sound does play through the speakers, but always about 4-5 seconds late. All sound starts late, stays lagging behind, and stops late after the mirroring ends. If I airplay just the sound to either ATV, everything works fine. It also works if I use airplay in-app: either airplaying a movie via QuickTime on the computer or playing a YouTube video by pressing the AirPlay button on the video on my iPhone. Everything also works when I send the audio to bluetooth headphones. So the problem is just with standard screen mirroring with two ATVs.

Does anyone have an idea what is going on? I have restarted all devices and reset both ATV's and generally fiddled around with plenty of settings, but to no avail. It is also not possible unfortunately to mirror the screen to one ATV and airplay the sound to another. Also, if I use the tiny speakers on the projector, everything again works fine, so it's somehow only the connection between the two ATVs when screen mirroring that produces the lag.

Posted on Oct 9, 2017 2:18 AM

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Answer 1

Rudegar

Level 10

179,886 points

Oct 9, 2017 8:17 AM in response to ToniTK

lots of people report that with bluetooth speakers both for atv and for other things like iOS devices and computers

the bluetooth profile called a2dp has no way of feedback it's progress or otherwise keep things in sync

so the appletv it's a fire and forget it has no idea how long the bluetooth device take to process the signal each speaker can take different time depending on the quality of the components and how much effort at signal quality filtering they perform.

also mirro of a high res computer across the network require some bandwidth so if you use it over 2.4Ghz a frequency bluetooth also use then network interference and because of that retransmit of data packets can cause visuals and audio to get out of sync

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Answer 2

ToniTK Author

Level 1

8 points

Nov 15, 2017 1:10 AM in response to Diana.McCall

Hi Diana and Rudegar,

thanks for the replies. I have finally gotten down to test the Apple TV using some other bluetooth audio device, namely headphones. I wanted to ask you to clarify if you really mean that it is impossible to mirror the screen to ATV so that the video output and audio output are distinct yet are guaranteed to remain (more or less) in sync. That's how I understood the answers.

But with my bluetooth headphones, everything works fine. So the ATV is capable of playing the video through a projector (in this case, my computer screen mirrored) while sending the audio to a bluetooth device perfectly in sync. But if I send the audio to the second ATV, connected directly by cable to speakers, a lag of several seconds (not milliseconds, mind you!) occurs. (Note also that video is not choppy, so bandwidth should suffice.) So the problem does not seem to be just bluetooth but the ATVs themselves, right? (Can it really be that the ATV takes something like 5-7 seconds to process a bluetooth input and output it via cable?)

This is an important question for me because, given that I cannot get the two ATVs setup to work, I wanted to buy new bluetooth speakers. Before I do that, it would be nice to know whether there will be a several seconds delay. I appreciate the responses, but I still wonder if there is an issue with my specific ATV rather than a systematic problem. Thanks!

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Answer 3

Oct 9, 2017 8:46 AM in response to ToniTK

Hi ToniTK. When you use basic AirPlay (in-app), the Apple TV is in control. It streams the audio/video content from the server and plays it by itself. Since there is a delay in transmitting the Bluetooth audio, it can roughly compensate for that by delaying the video slightly.

When you use mirroring, none of this is possible. Apple TV has to update the screen as soon as it is received, because it doesn't know whether it's an interactive display or just a video. So it cannot compensate for the Bluetooth delay. You should be able to use basic AirPlay for most content, so you can avoid mirroring.

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Answer 4

Nov 15, 2017 5:48 AM in response to ToniTK

When you send the audio output to a Bluetooth receiver "connected" to Apple TV, Apple TV can compensate for any delay in Bluetooth transmission. When you send the audio output to another Apple TV, you're using a second AirPlay link, not Bluetooth. Apple TV collects the audio into packets and sends them to the router, which relays them to the second Apple TV, which unpacks them and plays the sound. Each of those steps introduces a delay over which there is no control. The audio transmissions also need to be fitted in between the mirroring packets.

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Answer 5

ToniTK Author

Level 1

8 points

Nov 15, 2017 5:56 AM in response to Diana.McCall

Thanks, that is helpful - so there is no way to send the sound via Bluetooth to the other ATV, but I should not have this problem if I use bluetooth speakers rather than ATV connected to speakers. Curious that Apple does not make it possible to sync ATVs like that, or indeed, to mirror the screen to one ATV and send the sound to another. What still bothers me though is that if my computer can stream video and sound via my router to an ATV essentially without a lag, how is it that the sound from one ATV through the same router takes 5-7 seconds, which is an eternity compared to common network lags. Are the ATVs designed not to communicate with each other?

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Answer 6

Nov 15, 2017 7:27 AM in response to ToniTK

When your computer streams video and audio, it sends an interleaved stream. When you ask Apple TV to forward the audio on to another Apple TV, it has to do all the additional processing I described, while displaying the video signal. I am a bit mystified by the 5 second delay you report, but I know nothing about your environment, or the content involved.

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