stitch.sh

#!/bin/bash

# Generate sorted list.txt
ls -1v *.webm | while IFS= read -r f; do
  escaped_filename=$(sed "s/'/'\\\\''/g" <<< "$f")
  echo "file '$escaped_filename'"
done > list.txt

# Concatenate files
ffmpeg -f concat -safe 0 -i list.txt -c copy output.webm

# Cleanup (optional)
rm list.txt