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fix: honor telnyxs per-call codec in bidirectional stream

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Telnyx's bidirectional stream uses different codecs per direction:
  - Dograh → Telnyx: what we declare via `stream_bidirectional_codec`
  - Telnyx → Dograh: whatever the PSTN leg negotiated (PCMA for UK,
    Europe, India termination; PCMU for US), announced as
    `media_format.encoding` on the WebSocket start message.

We hardcoded both directions on the serializer to PCMU, so any call
whose PSTN leg used PCMA arrived as A-law bytes that we decoded
through a μ-law table → static for the entire call.

`handle_websocket` now extracts `media_format.encoding` from the
start message and threads it through `transport_kwargs`. The
serializer uses it for the Telnyx → Dograh direction; the
Dograh → Telnyx direction stays pinned to PCMU to match the
unchanged `stream_bidirectional_codec` in the dial/answer payloads.

Note: pipecat's `TelnyxFrameSerializer` names its params from the
call's POV, not Dograh's — `inbound_encoding` is what we send into
the call, `outbound_encoding` is what we receive. Easy to mix up.
This commit is contained in:
Sabiha Khan 2026-04-29 19:05:06 +05:30
parent 983b9bee71
commit 5ee68f58bb
2 changed files with 17 additions and 4 deletions
Download patch file Download diff file Expand all files Collapse all files

12
api/services/telephony/providers/telnyx/provider.py
View file

@ -82,6 +82,9 @@ class TelnyxProvider(TelephonyProvider):
f"{backend_endpoint}/api/v1/telephony/telnyx/events/{workflow_run_id}"
)
# stream_bidirectional_codec controls only the Dograh → Telnyx direction.
# The Telnyx → Dograh direction follows the PSTN leg and is announced via
# media_format.encoding in the WebSocket start message.
payload = {
"connection_id": self.connection_id,
"to": to_number,
@ -268,11 +271,15 @@ class TelnyxProvider(TelephonyProvider):
await websocket.close(code=4400, reason="Expected start event")
return
# Extract Telnyx-specific identifiers
# media_format.encoding is the codec Telnyx delivers on the
# inbound direction (Telnyx → Dograh); the outbound direction is
# pinned to PCMU separately via stream_bidirectional_codec.
try:
stream_id = start_data.get("stream_id", "")
start_info = start_data.get("start", {})
call_control_id = start_info.get("call_control_id", "")
media_format = start_info.get("media_format") or {}
encoding = media_format.get("encoding") or "PCMU"
except (KeyError, AttributeError):
logger.error("Missing stream_id or call_control_id in start message")
await websocket.close(code=4400, reason="Missing stream identifiers")
@ -288,7 +295,7 @@ class TelnyxProvider(TelephonyProvider):
logger.info(
f"Telnyx stream started: stream_id={stream_id}, "
f"call_control_id={call_control_id}"
f"call_control_id={call_control_id}, encoding={encoding}"
)
await run_pipeline_telephony(
@ -301,6 +308,7 @@ class TelnyxProvider(TelephonyProvider):
transport_kwargs={
"stream_id": stream_id,
"call_control_id": call_control_id,
"encoding": encoding,
},
)

9
api/services/telephony/providers/telnyx/transport.py
View file

@ -24,6 +24,7 @@ async def create_transport(
telephony_configuration_id: int | None = None,
stream_id: str,
call_control_id: str,
encoding: str = "PCMU",
):
"""Create a transport for Telnyx connections."""
config = await load_credentials_for_transport(
@ -36,12 +37,16 @@ async def create_transport(
f"Incomplete Telnyx configuration for organization {organization_id}"
)
# Pipecat's TelnyxFrameSerializer names its params from the call's POV,
# not Dograh's: ``inbound_encoding`` is what we *send into the call*
# (Dograh → Telnyx), and ``outbound_encoding`` is what we *receive out of
# the call* (Telnyx → Dograh).
serializer = TelnyxFrameSerializer(
stream_id=stream_id,
call_control_id=call_control_id,
api_key=api_key,
outbound_encoding="PCMU",
inbound_encoding="PCMU",
inbound_encoding="PCMU", # Dograh → Telnyx; matches stream_bidirectional_codec
outbound_encoding=encoding, # Telnyx → Dograh; from media_format.encoding
)
mixer = await build_audio_out_mixer(