[Question] How to get the HF audio?

[anunay1]

Hi,

I want to use the solution to emulate a HFP headset. I am using a USB BT Adpater(TP-Link). I am able to simulate a set of AT commands like Answer, handup, or voice recognization,. But when I answer the call I do not get the call audio. How do I achieve call audio?

[barbibulle]

Hi. Unfortunately, the current implementation of the HFP profile only supports the signaling layer (simulating answering a call, pressing buttons, ...) but not the audio path. The A2DP profile does support audio, but sadly that's a completely different audio protocol than HFP. HFP audio is exchanged over SCO channels (not ACL), which most controllers only support via side channels (i.e not over HCI). There is a standard for sending/receiving SCO data over HCI, but we have not implemented it yet. It is on the short term roadmap though.

[anunay1]

Thanks a ton for prompt response. It will be of great help if you can also share the short term roadmap.

[Robert-K]

Any updates on this? 😅

[zxzxwu]

We already completed the host side support in #254, you can check the example here: https://github.com/google/bumble/blame/e47cb5512c2ab5aabf8669f991362864acaa33a6/examples/run_hfp_gateway.py#L97

However, most of USB dongles still don't properly support eSCO and SCO over HCI. This is limited on the controller side because they just want to compat Windows. We cannot do anything here.

[barbibulle]

I haven't yet found a USB dongle that supports SCO over HCI. Most chipsets have FW that's designed to send audio data via a side channel (typically I2S). If anyone knows of a USB dongle or dev board that can support SCO over HCI, let me know, I'd love to test that.

[Robert-K]

This repo implements bluetooth HFP on a Raspberry Pi and even suggests using USB dongles for better reliablility. Tbh I don't fully understand the HCI part, so my apologies if it's not relevant.

I'm just trying to turn a Tischfernsprecher W48 into an HFP device, but most HFP implementations are abandoned/deprecated :/

[barbibulle]

Actually, now that my memory is somewhat refreshed, I recall that the issue I ran into was that support for USB isochronous endpoints via the Python bindings for libsub wasn't quite working as expected. Since SCO packets over HCI/USB are transferred via isosynchronous endpoints (as opposed to bulk endpoints for ACL data), that was a blocker. I will revisit that with the latest version of the lib to see if I can make it work.

[Robert-K]

Looking forward to it!
In the meantime I'll try to accomplish my goals using an ESP32 and the newly released walinsky/a2dpSinkHfpClient 🚀