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Bluetooth Profile Support - iOS Audio, Browsing, Metadata...

Discussion in 'Model S: User Interface' started by Adam Gill, Jun 27, 2015.

  1. Adam Gill

    Adam Gill New Member

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    Does anyone know how much of the A2DP and AVRCP Bluetooth profiles are currently supported by the MS?
    I'm specifically wondering about sections 2.2.4 and 2.2.5 of Apple's iOS Bluetooth Design Guidelines PDF
    Specifically, is AAC audio streaming supported? Browsing and metadata supported?
     
  2. Korben

    Korben Member

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    Looks like AAC is supported (this is a snapshot of a message received from the car). No APTX though :(, it should show up as non-a2dp.

    Capture.PNG
     
  3. ra-san

    ra-san Member

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    Agree that AAC is supported in the Bluetooth profile. Had others disagree for ages, but as your snapshot shows, as my ears say, and as I've had confirmed from inside Tesla, it does.

    That said, last I looked into it, on the iOS side, what I found was that any audio going through Bluetooth is first decoded to raw, then recompressed to the Bluetooth link negotiated. This means unfortunately that even though AAC is supported, you'll still have some additional transcoding loss even when using AAC audio files on your device. It doesn't send the AAC frames from the file itself. Far as I can see, the spec allows that it could, it's just that the implementation doesn't.
    Would love to be wrong. And it's still a huge step up in sound quality over the base Bluetooth codec.
     
  4. Adam Gill

    Adam Gill New Member

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    Thanks Korben, that's exactly what I was looking for. How do you get that capture?
     
  5. Korben

    Korben Member

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    An android phone and wireshark will do the trick.

    Turn on bluetooth logging in an android phone (developer options IIRC) and after connecting to your car and using various bluetooth functions copy the "btsnoop_hci.log" file from your phone to your computer. If you open it up in wireshark it will work just like a regular pcap.

    The message above is part of capabilities negotiation (sent by the parrot on the Tesla). There are several of these sent, I just shared one of the AAC messages.
     
  6. wayner

    wayner Active Member

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    Any idea what Bluetooth bitrate is used between an iPhone 6+ and MS?
     
  7. ra-san

    ra-san Member

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    264,830bps is what the Bluetooth Design Guidelines linked above states, which is also the doc I referred to when I had posted about this on other threads. It does also state that the device should support variable bit rates, but that seems to be to handle switched from playing music to playing other chunks of sound from the phone (like notifications, etc.), rather than for handling direct playing of sound file bitstreams.

    I've just seen this from the doc and from what I've gleaned from others that have looked into Bluetooth handling AAC for other devices. I haven't personally seen the negotiated link in a Bluetooth logging setup to confirm that's the bitrate, and that it doesn't vary from song to song.
     

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