BaseOutputTransport: implement generic write_dtmf()

CHANGELOG.md

@@ -7,6 +7,12 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+## Added
+
+- `BaseOutputTransport` now implements `write_dtmf()` by loading DTMF audio and
+  sending it through the transport. This makes sending DTMF generic across all
+  output transports.
+
 ## Changed
 
 - `pipecat.frames.frames.KeypadEntry` is deprecated and has been moved to

src/pipecat/transports/base_output.py

@@ -19,6 +19,7 @@ from typing import Any, AsyncGenerator, Dict, List, Mapping, Optional
 from loguru import logger
 from PIL import Image
 
+from pipecat.audio.dtmf.utils import load_dtmf_audio
 from pipecat.audio.mixers.base_audio_mixer import BaseAudioMixer
 from pipecat.audio.utils import create_stream_resampler, is_silence
 from pipecat.frames.frames import (
@@ -223,7 +224,12 @@ class BaseOutputTransport(FrameProcessor):
         Args:
             frame: The DTMF frame to write.
         """
-        pass
+        dtmf_audio = await load_dtmf_audio(frame.button, sample_rate=self._sample_rate)
+        dtmf_audio_frame = OutputAudioRawFrame(
+            audio=dtmf_audio, sample_rate=self._sample_rate, num_channels=1
+        )
+        dtmf_audio_frame.transport_destination = frame.transport_destination
+        await self.write_audio_frame(dtmf_audio_frame)
 
     async def send_audio(self, frame: OutputAudioRawFrame):
         """Send an audio frame downstream.