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Audio Tools Node implementations

Here some brief details as how the functionality is implemented.

audio_capture_node

Audio Capture Node using SDL2 for ROS 2

Captures raw audio from an input device and publishes it via ROS topics. Useful for audio processing pipelines, speech recognition, or diagnostics.

✅ Topics

Topic Type Description
/audio audio_tools/msg/AudioData Raw audio byte stream
/audio_stamped audio_tools/msg/AudioDataStamped Audio with timestamp + info
/audio_info audio_tools/msg/AudioInfo Metadata (sample rate, format, etc.)

⚙️ Parameters

Name Type Default Description
sample_format string S16LE Audio format (S16LE, F32LE, etc.)
channels int 1 Number of channels (1–8)
sample_rate int 16000 Sampling rate in Hz
device int -1 Device index (-1 = default input device)
chunk_size int 1024 Buffer size per capture call (512–4096)

📦 Message Notes

  • AudioData: raw uint8[] data
  • AudioDataStamped:
  • std_msgs/Header header with stamp and frame_id
  • AudioData audio
  • AudioInfo info
  • AudioInfo includes:
  • sample_rate
  • sample_format
  • channels

🧩 Implementation Notes

  • Uses SDL2 for low-latency cross-platform audio capture.
  • Device info is printed on startup.
  • Buffer timestamping is calculated based on sample rate and byte depth.
  • Publishes metadata (/audio_info) every 5 seconds.
  • All audio capture runs on a callback triggered by SDL2.

🏁 Launch Example

ros2 run audio_tools audio_capture_node \
  --ros-args \
  -p sample_rate:=16000 \
  -p channels:=1 \
  -p device:=-1

🧪 Dependencies

  • rclcpp
  • SDL2
  • Custom messages in audio_tools

audio_playback_node

Audio Playback Node using SDL2 for ROS 2

Subscribes to audio messages and plays them in real-time through an output device using SDL2.

✅ Topics

Topic Type Description
/audio_playback (default) audio_tools/msg/AudioDataStamped Audio stream with metadata

⚙️ Parameters

Name Type Default Description
audio_topic string /audio_playback Topic to subscribe to for audio data
device_index int -1 Index of output device (-1 = default device)

📦 Expected Message Format

  • AudioDataStamped:
  • AudioData audio: raw audio byte stream
  • AudioInfo info: playback metadata:
    • sample_rate
    • sample_format
    • channels

🧩 Implementation Notes

  • Uses SDL2 to output audio through a selected or default device.
  • Supports multiple formats: S16LE, S16BE, U8, S8, F32LE, F32BE
  • Device info printed on startup.
  • Initializes playback only on receiving the first message (lazy init).
  • Queues audio chunks using SDL_QueueAudio().

🏁 Launch Example

ros2 run audio_tools audio_playback_node \
  --ros-args \
  -p audio_topic:=/audio_stamped \
  -p device_index:=-1

🧪 Dependencies

  • rclcpp
  • SDL2
  • Custom messages in audio_tools

vad_node

Voice Activity Detection Node for ROS 2

Analyzes audio streams to detect the presence of speech or voice activity and publishes the detection state. Useful for conversation systems, wake word triggers, and audio recording automation.

✅ Topics

Topic Type Description
/voice_activity audio_tools/msg/VoiceActivity Voice activity detection state
Subscribes to:
/audio_stamped audio_tools/msg/AudioDataStamped Audio input for analysis
---

⚙️ Parameters

Name Type Default Description
energy_threshold float 0.01 Detection sensitivity threshold
hold_time float 0.5 Time in seconds to maintain detection after voice stops
min_samples int 160 Minimum samples needed for detection decision
---

📦 Message Notes

  • VoiceActivity:
  • std_msgs/Header header with stamp and frame_id
  • bool active - Detection state (true/false)
  • float32 energy_level - Current audio energy level
  • float32 threshold - Detection threshold in use
  • float32 hold_time - Time to hold detection state after voice stops

🧩 Implementation Notes

  • Uses an energy-based algorithm for voice detection.
  • Converts all audio formats to normalized float [-1.0, 1.0] for processing.
  • Energy calculation: energy = sum(sample * sample) / num_samples
  • Hold timer prevents rapid switching between states during pauses.
  • Format conversion supports U8, S8, S16LE, S16BE, F32, etc.

🏁 Launch Example

ros2 run audio_tools vad_node \
 --ros-args \
-p energy_threshold:=0.015 \
-p hold_time:=0.7 \
-p min_samples:=160

🧪 Dependencies

  • rclcpp
  • audio_tools/msg/AudioDataStamped
  • audio_tools/msg/VoiceActivity