One-drop splitter for RØDECaster Pro (fw 2.x) poly-WAVs. Outputs mono stems for selected mics (defaults: Mic1=ch2, Mic2=ch3). macOS Shortcuts-friendly; logs to /tmp/rode_split.log. Includes a “channel finder” mode to discover which channel index your mics are on.

wavspit.sh

#!/bin/bash
# Split RØDECaster Pro multitrack poly-WAVs into per-channel stems (macOS Shortcuts friendly)
# -----------------------------------------------------------------------------
# REQUIREMENTS
#   - ffmpeg & ffprobe installed (e.g., Homebrew: `brew install ffmpeg`)
#
# DEFAULTS (tuned for RØDECaster Pro 1, fw 2.1.x)
#   - Mic 1 is on channel index 2 (zero-based; i.e., 3rd channel in the file)
#   - Mic 2 is on channel index 3
#   - Outputs go to a single sibling folder named "split"
#
# QUICK USE
#   bash rodecaster_split.sh /path/to/file.wav
#
# TWEAKS (set as environment variables, or edit below)
#   MIC1_CH_INDEX   : default 2   (e.g., MIC1_CH_INDEX=0 for first channel)
#   MIC2_CH_INDEX   : default 3
#   NAME1 / NAME2   : default mic1 / mic2 (e.g., NAME1=host NAME2=guest)
#   OUTDIR_NAME     : default split
#   INCLUDE_STEREO  : default false  (set to true to also export stereo mix as one stereo file)
#   FIND_CHANNELS   : default false  (set to true to export 3-second previews for *every* channel)
#   NORM            : default false  (set to true to add EBU R128 loudness normalization per mic)
#
# EXAMPLES
#   # Use different mapping (e.g., mics on ch0 and ch1), and friendly names:
#   MIC1_CH_INDEX=0 MIC2_CH_INDEX=1 NAME1=host NAME2=guest bash rodecaster_split.sh file.wav
#
#   # Also export the stereo mix and run loudness normalization:
#   INCLUDE_STEREO=true NORM=true bash rodecaster_split.sh file.wav
#
#   # Not sure which channels your mics are on? Generate 3s previews of every channel:
#   FIND_CHANNELS=true bash rodecaster_split.sh file.wav
#
# NOTES
#   - Works inside macOS Shortcuts: set shell to /bin/bash, pass input "as arguments".
#   - Logs to /tmp/rode_split.log
#   - Uses ffmpeg pan filter (works on more builds than -map_channel).
# -----------------------------------------------------------------------------

set -euo pipefail

# Ensure Homebrew binaries are visible (important when run via Shortcuts)
export PATH="/opt/homebrew/bin:/usr/local/bin:$PATH"

FFMPEG="${FFMPEG_PATH:-$(command -v ffmpeg || true)}"
FFPROBE="${FFPROBE_PATH:-$(command -v ffprobe || true)}"
LOG="/tmp/rode_split.log"

# ---- CONFIG ----
MIC1_CH_INDEX="${MIC1_CH_INDEX:-2}"      # zero-based channel index for Mic 1
MIC2_CH_INDEX="${MIC2_CH_INDEX:-3}"      # zero-based channel index for Mic 2
NAME1="${NAME1:-mic1}"                   # suffix label for Mic 1 output
NAME2="${NAME2:-mic2}"                   # suffix label for Mic 2 output
OUTDIR_NAME="${OUTDIR_NAME:-split}"      # shared output folder
INCLUDE_STEREO="${INCLUDE_STEREO:-false}"# true|false -> also export stereo mix
FIND_CHANNELS="${FIND_CHANNELS:-false}"  # true|false -> export 3s previews for each channel
NORM="${NORM:-false}"                    # true|false -> apply EBU loudness normalization

# Loudness settings (used if NORM=true)
# Target dialog norm around podcast standards; tweak as desired.
LOUD_I="${LOUD_I:--16}"
LOUD_TP="${LOUD_TP:--1.5}"
LOUD_LRA="${LOUD_LRA:-11}"

if [[ -z "$FFMPEG" || -z "$FFPROBE" ]]; then
  echo "ffmpeg/ffprobe not found on PATH" >> "$LOG"
  echo "Install with: brew install ffmpeg"
  exit 1
fi

for f in "$@"; do
  [[ -f "$f" ]] || { echo "Skip (not a file): $f" >> "$LOG"; continue; }

  # Case-insensitive .wav check (Bash 3.2 compatible)
  ext="${f##*.}"
  shopt -s nocasematch
  if [[ ! "$ext" =~ ^wav$ ]]; then
    shopt -u nocasematch
    echo "Skip non-WAV: $f" >> "$LOG"
    continue
  fi
  shopt -u nocasematch

  dir="$(cd "$(dirname "$f")" && pwd)"
  base="$(basename "$f")"
  name="${base%.*}"

  outdir="$dir/$OUTDIR_NAME"
  mkdir -p "$outdir"

  # Probe channel count
  channels="$("$FFPROBE" -v error -select_streams a:0 -show_entries stream=channels \
             -of default=nw=1:nk=1 "$f" | tr -d '[:space:]' || true)"
  echo "[$(date)] $base → channels=$channels" >> "$LOG"

  if [[ ! "$channels" =~ ^[0-9]+$ ]]; then
    echo "No channel info from ffprobe, skipping: $f" >> "$LOG"
    continue
  fi

  # Optional: FIND_CHANNELS preview (3s mono WAV for each channel)
  if [[ "$FIND_CHANNELS" == "true" ]]; then
    i=0
    while [ "$i" -lt "$channels" ]; do
      "$FFMPEG" -hide_banner -loglevel error -y -t 3 -i "$f" \
        -filter_complex "[0:a]pan=mono|c0=c${i}[ch]" \
        -map "[ch]" -c:a pcm_s16le "$outdir/${name}_ch${i}_preview.wav"
      i=$((i+1))
    done
    echo "Preview stems written under: $outdir" >> "$LOG"
    # Continue to full export as well (comment 'continue' in if you only want previews)
  fi

  # Guard against out-of-range channel indexes
  if (( MIC1_CH_INDEX >= channels || MIC2_CH_INDEX >= channels )); then
    echo "Not enough channels ($channels) for indexes $MIC1_CH_INDEX/$MIC2_CH_INDEX in $base" >> "$LOG"
    continue
  fi

  # Optional: export stereo mix as a single stereo file (uses c0/c1)
  if [[ "$INCLUDE_STEREO" == "true" && "$channels" -ge 2 ]]; then
    "$FFMPEG" -hide_banner -loglevel error -y -i "$f" \
      -filter_complex "[0:a]pan=stereo|c0=c0|c1=c1[st]" \
      -map "[st]" -c:a pcm_s24le "$outdir/${name}_stereo_mix.wav"
  fi

  # Build optional loudness filter
  norm_filter=""
  if [[ "$NORM" == "true" ]]; then
    norm_filter=",loudnorm=I=$LOUD_I:TP=$LOUD_TP:LRA=$LOUD_LRA"
  fi

  # MIC 1
  "$FFMPEG" -hide_banner -loglevel error -y -i "$f" \
    -filter_complex "[0:a]pan=mono|c0=c${MIC1_CH_INDEX}${norm_filter}[m1]" \
    -map "[m1]" -c:a pcm_s24le "$outdir/${name}_${NAME1}.wav"

  # MIC 2
  "$FFMPEG" -hide_banner -loglevel error -y -i "$f" \
    -filter_complex "[0:a]pan=mono|c0=c${MIC2_CH_INDEX}${norm_filter}[m2]" \
    -map "[m2]" -c:a pcm_s24le "$outdir/${name}_${NAME2}.wav"

  echo "Wrote: $outdir/${name}_${NAME1}.wav, ${name}_${NAME2}.wav" >> "$LOG"
done

echo "OK"