usb-autovolume

#!/bin/bash
# Configuration
readonly DEFAULT_VOLUME=85                   # Default volume to set for USB soundcard

# Enable strict error handling
set -euo pipefail

# Function to handle errors
# Logs an error message with the line number and error code, then exits
# Arguments:
#   $1 - Line number where the error occurred
#   $2 - Error code returned by the command
error_handler() {
    local line_no=$1
    local error_code=$2
    log_message "Error (code: ${error_code}) occurred on line ${line_no}"
    exit ${error_code}
}

# Trap any error and pass it to the error handler
trap 'error_handler ${LINENO} $?' ERR

# Log function to write messages to a log file
# This appends messages with a timestamp to /tmp/autovolume-usb.log
# Arguments:
#   $1 - Message to log
log_message() {
    echo "$1"
    echo "$(date) - $1" >> /tmp/autovolume-usb.log
}

# Sleep for a brief moment to ensure the device is fully initialized
sleep 1

# Log the detected soundcards
log_message "$(aplay -l)"

# Check for USB soundcard
# NOTE: If there are multiple USB cards detected, we assume the last entry is the intended one
# This resolves ambiguity if multiple USB soundcards are detected
# TODO - pass env vars from udev so this isnt ambiguous, keep this method as fallback
USB_CARDS=$(aplay -l | grep "card" | grep -i "usb" | awk '{print $2}' | cut -d':' -f1)
if [ -n "$USB_CARDS" ]; then
    # If multiple USB soundcards are detected, log a warning and pick the last one
    CARD_COUNT=$(echo "$USB_CARDS" | wc -l)
    if [ "$CARD_COUNT" -gt 1 ]; then
        log_message "Warning: Multiple USB soundcards detected. Using the last detected card."
    fi

    # Select the last USB soundcard detected
    USB_CARD=$(echo "$USB_CARDS" | tail -n 1)

    # Output the soundcard index for debugging
    log_message "USB audio device detected. Soundcard index: $USB_CARD"

    # Validate USB_CARD is numeric
    if ! [[ "$USB_CARD" =~ ^[0-9]+$ ]]; then
        log_message "Error: Invalid soundcard number: $USB_CARD"
        exit 1
    fi

    # Detect the control name for the USB soundcard, like 'Master', 'Speaker', etc.
    CONTROL_NAME=$(amixer -c "$USB_CARD" scontrols | grep -i 'Master\|Speaker\|Headphone\|Front\|Output\|PCM' | head -n 1 | cut -d"'" -f2)

    # If no known control found, log an error
    if [ -z "$CONTROL_NAME" ]; then
        log_message "No valid control name found for USB soundcard (card $USB_CARD)"
        exit 1
    fi

    log_message "Mixer name: $CONTROL_NAME"

    # Adjust the volume of the detected soundcard to 85% using amixer
    amixer -c "$USB_CARD" sset "$CONTROL_NAME" "$DEFAULT_VOLUME%"

    log_message "Volume set to $DEFAULT_VOLUME% on card $USB_CARD, control '$CONTROL_NAME'"
else
    log_message "No USB audio device detected."
fi