84 lines
2.6 KiB
Markdown
84 lines
2.6 KiB
Markdown
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---
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title: Projects
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---
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### AAC observations
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The following are the observations from the Wireshark capture traces regarding the issue observed while using AAC with SRS-XB33.
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1. Android and SRS-XB33
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- Remote sends `GetAllCapabilities` command and gets `SBC`, `MPEG-2/4 AAC` and `LDAC` as supported in the response.
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- In case of `AAC`, the following flags are set on Android side
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- MPEG-2 AAC LC
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- Sampling rate of 44.1 KHz
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- VBR supported
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- 2 channels
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- The `SetConfiguration` gets send with the following parameters set
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- MPEG-2 AAC LC
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- Sampling rate of 44.1 KHz
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- VBR supported
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- 2 channels
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2. PulseAudio and SRS-XB33
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1. Initial Connection
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- The device sends a `Discover` request, followed by `GetAllCapabilities` and then `SetConfiguration`.
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- For the `GetAllCapabilities`, `MPEG-2,4 AAC` and `SBC` are returned by bluez.
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- The `GetAllCapabilities` command, seems to be send twice from the device and in both cases return the exact same capabilities. This happens for both `AAC` and `SBC`.
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- The `SetConfiguration` command send is send by SRS-XB33 and has the following parameters set
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- MPEG-4 AAC LC
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- Sampling rate of 48 KHz
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- 2 channels
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- VBR not supported
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2. Reconnection
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In the reconnection case, the `SetConfiguration` command has the following parameters set.
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- Sampling rate of 44.1 KHz
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- MPEG-4 AAC LC
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- 2 channels
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- VBR not supported
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### Codec switching
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- Currently the following profiles exist
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1. headset<sub>audiogateway</sub>
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2. headset<sub>headunit</sub>
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3. a2dp<sub>source</sub>
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4. a2dp<sub>sink</sub>
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- For backchannel, two additional profiles are needed
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1. a2dp<sub>sourcewithbackchannel</sub>
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2. a2dp<sub>sinkwithbackchannel</sub>
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- Each profile has it's own codec. However, one problem to solve is, one codec for one direction and a different codec for the other direction. For eg. aptX-LL uses aptX for playback and SBC for recording. How to solve this? Is introducing the backchannel profiles, be sufficient to take care of this?
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### Under the hood
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- https://gavv.github.io/articles/pulseaudio-under-the-hood
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### Bluetooth testing
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``` bash
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./simple-endpoint 2C:DB:07:58:F2:F9 ldacsource
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./test-device connect 4C:BC:98:80:01:9B "0000110b-0000-1000-8000-00805f9b34fb"
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env GST_DEBUG=3 gst-launch-1.0 audiotestsrc ! ldacenc ! a2dpsink transport=/org/bluez/hci0/dev_4C_BC_98_80_01_9B/sep10/fd0
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```
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## Module loop back
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- https://endless.ersoft.org/pulseaudio-loopback/
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