audio processing with examples

[eliteprox]

This pull request introduces a new audio effects processing example and enhances the pytrickle client to provide robust fallback behavior for audio and video frame processing. It also updates dependencies and improves the handling of audio processing failures to ensure that frames are never skipped.

Key changes:

New Example and Dependencies

• Added a new example process_audio_example.py showcasing real-time audio effects (volume, echo, low-pass filter) with PyTrickle, including parameter updates and logging.
• Updated requirements.txt to include scipy for audio processing in examples.

Client Fallback and Robustness Improvements

• Enhanced pytrickle/client.py to cache the last successfully processed audio and video frames, and to provide smart fallback frames when processing fails or returns None. This ensures continuity in streaming applications. [1] [2]
• In the audio ingress loop, now always sends an audio frame (original frame as fallback) even if processing fails, preventing dropped frames.

Code Quality and Typing

• Improved typing in pytrickle/client.py by importing and using List for audio frame lists.

Cleanup

• Removed unused comments and code sections from pytrickle/frames.py for clarity.