import re


def GetBitstreamVersion(aBitstreamFile):
    """Extract version number from given bitstream file."""
    f = open(aBitstreamFile, 'rt')
    data = f.read()
    f.close()
    ver = re.search(r'[0-9]+\.[0-9]+\.[0-9]+', data)
    if ver:
        return ver.group(0)
    return 'Unknown'