v0.0.53

### Added

- Added `ElevenLabsHttpTTSService` which uses EleveLabs' HTTP API instead of the websocket one.

- Introduced pipeline frame observers. Observers can view all the frames that go through the pipeline without the need to inject processors in the pipeline. This can be useful, for example, to implement frame loggers or debuggers among other things. The example `examples/foundational/30-observer.py` shows how to add an observer to a pipeline for debugging.

- Introduced heartbeat frames. The pipeline task can now push periodic heartbeats down the pipeline when `enable_heartbeats=True`. Heartbeats are system frames that are supposed to make it all the way to the end of the pipeline. When a heartbeat frame is received the traversing time (i.e. the time it took to go through the whole pipeline) will be displayed (with TRACE logging) otherwise a warning will be shown. The example `examples/foundational/31-heartbeats.py` shows how to enable heartbeats and forces warnings to be displayed.

- Added `LLMTextFrame` and `TTSTextFrame` which should be pushed by LLM and TTS services respectively instead of `TextFrame`s.

- Added `OpenRouter` for OpenRouter integration with an OpenAI-compatible interface. Added foundational example `14m-function-calling-openrouter.py`.

- Added a new `WebsocketService` based class for TTS services, containing base functions and retry logic.

- Added `DeepSeekLLMService` for DeepSeek integration with an OpenAI-compatible interface. Added foundational example `14l-function-calling-deepseek.py`.

- Added `FunctionCallResultProperties` dataclass to provide a structured way to control function call behavior, including:
  - `run_llm`: Controls whether to trigger LLM completion
  - `on_context_updated`: Optional callback triggered after context update

- Added a new foundational example `07e-interruptible-playht-http.py` for easy testing of `PlayHTHttpTTSService`.

- Added support for Google TTS Journey voices in `GoogleTTSService`.

- Added `29-livekit-audio-chat.py`, as a new foundational examples for `LiveKitTransportLayer`.

- Added `enable_prejoin_ui`, `max_participants` and `start_video_off` params to `DailyRoomProperties`.

- Added `session_timeout` to `FastAPIWebsocketTransport` and `WebsocketServerTransport` for configuring session timeouts (in seconds). Triggers `on_session_timeout` for custom timeout handling.
  See [examples/websocket-server/bot.py](https://github.com/pipecat-ai/pipecat/blob/main/examples/websocket-server/bot.py).

- Added the new modalities option and helper function to set Gemini output modalities.

- Added `examples/foundational/26d-gemini-multimodal-live-text.py` which is using Gemini as TEXT modality and using another TTS provider for TTS process.

### Changed

- Modified `UserIdleProcessor` to start monitoring only after first conversation activity (`UserStartedSpeakingFrame` or `BotStartedSpeakingFrame`) instead of immediately.

- Modified `OpenAIAssistantContextAggregator` to support controlled completions and to emit context update callbacks via `FunctionCallResultProperties`.

- Added `aws_session_token` to the `PollyTTSService`.

- Changed the default model for `PlayHTHttpTTSService` to `Play3.0-mini-http`.

- `api_key`, `aws_access_key_id` and `region` are no longer required parameters for the PollyTTSService (AWSTTSService)

- Added `session_timeout` example in `examples/websocket-server/bot.py` to handle session timeout event.

- Changed `InputParams` in `src/pipecat/services/gemini_multimodal_live/gemini.py` to support different modalities.

- Changed `DeepgramSTTService` to send `finalize` event whenever VAD detects `UserStoppedSpeakingFrame`. This helps in faster transcriptions and clearing the `Deepgram` audio buffer.

### Fixed

- Fixed an issue where `DeepgramSTTService` was not generating metrics using pipeline's VAD.

- Fixed `UserIdleProcessor` not properly propagating `EndFrame`s through the pipeline.

- Fixed an issue where websocket based TTS services could incorrectly terminate their connection due to a retry counter not resetting.

- Fixed a `PipelineTask` issue that would cause a dangling task after stopping the pipeline with an `EndFrame`.

- Fixed an import issue for `PlayHTHttpTTSService`.

- Fixed an issue where languages couldn't be used with the `PlayHTHttpTTSService`.

- Fixed an issue where `OpenAIRealtimeBetaLLMService` audio chunks were hitting an error when truncating audio content.

- Fixed an issue where setting the voice and model for `RimeHttpTTSService` wasn't working.

- Fixed an issue where `IdleFrameProcessor` and `UserIdleProcessor` were getting initialized before the start of the pipeline.