Bluetooth latency

  1. rantrile
    The audio is not transferred instantly between bluetooth transmitting device and a bluetooth device that receives the signal. Therefore when I'm watching movies on my Android TV box the audio is not being synced to the video.

    The app that plays movies allow me to enter offset audio in milliseconds. I would like to know what value should I enter in order to have audio and video in sync.

    My current setup is Leelbox Android TV box that uses Bluetooth 4.0 and Fiio BTR1 Bluetooth amp.

    I also wonder whether the Bluetooth delay depends on the transmitting device, receiving device or both? Or there is a standard delay for Bluetooth 4.0 SBC and it is constant between all devices?
     
  2. subtec
    Latency depends on the codec being used:

    [​IMG]

    SBC is the standard Bluetooth codec for stereo audio, and no doubt what you're using. The codec must be supported by both the transmitter and receiver. The BTR1 supports AptX and AptX-LL, but your TV box doesn't seem to support anything other than SBC, so that's what it reverts to. You'll have to get a different transmitter that supports AptX(-LL) for better latency.
     
  3. rantrile
    Well, since my concern is only about watching movies, SBC latency would be fine for as long as I can nail the correct delay.
    However,
    1) I don't understand what is +-50ms means? It depends on what?
    2) I already seen this table and tried to set delay to 170ms, 220ms, and 270ms and also in between these values, and for some reason I still can't nail it. The voice is always not in sync with the lips, but it becomes difficult to say whether it's behind or forward once the difference of the delay is not significant. Is there any test video or technique that can be used?
    3) Do you think it would matter what particular devices are being used for transmitting and receiving (not what I expect, but will ask anyway) or for as long as the connection is SBC Bluetooth 4.0 the delay should be just that as stated?

    Thank you
     
  4. subtec
    It means just what it says: plus or minus 50ms. So for SBC the latency could be anything from 170-270ms.

    I could only guess at what exactly determines this, but it probably has to do with wifi congestion and/or complexity of the audio being encoded.

    I doubt you'll get much better with standard SBC. AptX-LL is what you want to get it as low as possible.
     
  5. rantrile
    I mean, what exactly determines the +-50ms? I couldn't find any info on that. I somewhat doubt it's wifi congestion or the audio complexity. But if it is audio complexity indeed, that would suck, as it would mean constant non-sync between video and audio.

    Well, for as long as watching saved movies I don't really care about how much the latency is. All I need to know is the correct value so I can adjust it in Kodi/MX player.
     
    Last edited: Jul 13, 2018 at 2:01 PM

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