import re


def extract_field_from_id3tool_out(id3tool_out, field_id):
    """
    Extracts a field from the id3tool output.
    """
    m = re.search(r'^'+field_id+r':\s*(.*)$', id3tool_out, re.MULTILINE)
    if m:
        return m.group(1)
    else:
        return None