tools: add audio normalize script example.

tools/normalize.py

+#!/usr/bin/env python2
+
+import sys, subprocess
+
+if len(sys.argv) > 1:
+    ifile  = sys.argv[1]
+    encopt = sys.argv[2:-1]
+    ofile  = sys.argv[-1]
+else:
+    print 'usage: %s <input> [encode_options] <output>' % sys.argv[0]
+    sys.exit(1)
+
+analysis_cmd  = 'ffprobe -v error -of compact=p=0:nk=1 '
+analysis_cmd += '-show_entries frame_tags=lavfi.r128.I -f lavfi '
+analysis_cmd += "amovie='%s',ebur128=metadata=1" % ifile
+try:
+    probe_out = subprocess.check_output(analysis_cmd, shell=True)
+except subprocess.CalledProcessError, e:
+    sys.exit(e.returncode)
+loudness = ref = -23
+for line in probe_out.splitlines():
+    sline = line.rstrip()
+    if sline:
+        loudness = sline
+adjust = ref - float(loudness)
+if abs(adjust) < 0.0001:
+    print 'No normalization needed for ' + ifile
+else:
+    print "Adjust %s by %.1fdB" % (ifile, adjust)
+    norm_cmd  = ['ffmpeg', '-i', ifile, '-af', 'volume=%fdB' % adjust]
+    norm_cmd += encopt + [ofile]
+    print ' => %s' % ' '.join(norm_cmd)
+    subprocess.call(norm_cmd)