feat: add video_out_codec parameter for DailyTransport (#3520)

* feat: add video_out_codec parameter for DailyTransport

Add video_out_codec parameter to TransportParams allowing configuration
of the preferred video codec (VP8, H264, H265) for video output.

When set, this passes the preferredCodec option to Daily's
VideoPublishingSettings during the join operation.

* chore: move video_out_codec parameter to changelog folder (#3522)

* Initial plan

* Move video_out_codec parameter to changelog/3520.added.md

Co-authored-by: jamsea <614910+jamsea@users.noreply.github.com>

* Revert all CHANGELOG.md changes, keep only changelog/3520.added.md

Co-authored-by: jamsea <614910+jamsea@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: jamsea <614910+jamsea@users.noreply.github.com>

---------

Co-authored-by: Copilot <198982749+Copilot@users.noreply.github.com>
Co-authored-by: jamsea <614910+jamsea@users.noreply.github.com>

src/pipecat/transports/base_transport.py

@@ -98,6 +98,7 @@ class TransportParams(BaseModel):
         video_out_bitrate: Video output bitrate in bits per second.
         video_out_framerate: Video output frame rate in FPS.
         video_out_color_format: Video output color format string.
+        video_out_codec: Preferred video codec for output (e.g., 'VP8', 'H264', 'H265').
         video_out_destinations: List of video output destination identifiers.
         vad_enabled: Enable Voice Activity Detection (deprecated).
 
@@ -151,6 +152,7 @@ class TransportParams(BaseModel):
     video_out_bitrate: int = 800000
     video_out_framerate: int = 30
     video_out_color_format: str = "RGB"
+    video_out_codec: Optional[str] = None
     video_out_destinations: List[str] = Field(default_factory=list)
     vad_enabled: bool = False
     vad_audio_passthrough: bool = False

src/pipecat/transports/daily/transport.py

@@ -811,6 +811,11 @@ class DailyTransportClient(EventHandler):
                     "camera": {
                         "sendSettings": {
                             "maxQuality": "low",
+                            **(
+                                {"preferredCodec": self._params.video_out_codec}
+                                if self._params.video_out_codec
+                                else {}
+                            ),
                             "encodings": {
                                 "low": {
                                     "maxBitrate": self._params.video_out_bitrate,