python-rgain (replaygain) fails when no ID3 tag is present

[joergsorge]

lsb_release -rd
Description: Ubuntu 14.04.4 LTS
Release: 14.04

apt-cache policy python-rgain
python-rgain:
  Installiert: 1.2-1
  Installationskandidat: 1.2-1

Hi,

a [replaygain --show file] by files without id3-Tag reports the Error, that is no ID3-Tag is present:
replaygain --show test.mp3
test.mp3
  <Error reading Replay Gain: ID3NoHeaderError(u"'test.mp3' doesn't start with an ID3 tag",)>

By trying to write a replay gain value, the full python stack trace is shown:
$ replaygain -f --no-album test.mp3
Calculating Replay Gain information ...
  test.mp3: -3.85 dB
Writing Replay Gain information to files ...
  test.mp3:
Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/rgain/script/replaygain.py", line 130, in do_gain
    formats_map.write_gain(filename, trackdata, albumdata)
  File "/usr/lib/python2.7/dist-packages/rgain/rgio.py", line 345, in write_gain
    accessor[1](filename, trackgain, albumgain)
  File "/usr/lib/python2.7/dist-packages/rgain/rgio.py", line 284, in mp3_default_write_gain
    mp3_legacy_write_gain(filename, trackdata, albumdata)
  File "/usr/lib/python2.7/dist-packages/rgain/rgio.py", line 159, in mp3_legacy_write_gain
    tags = ID3(filename)
  File "/usr/lib/python2.7/dist-packages/mutagen/id3.py", line 73, in __init__
    super(ID3, self).__init__(*args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/mutagen/_util.py", line 120, in __init__
    super(DictProxy, self).__init__(*args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/mutagen/__init__.py", line 42, in __init__
    self.load(*args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/mutagen/id3.py", line 121, in load
    self.__load_header()
  File "/usr/lib/python2.7/dist-packages/mutagen/id3.py", line 239, in __load_header
    raise ID3NoHeaderError("'%s' doesn't start with an ID3 tag" % fn)
ID3NoHeaderError: 'test.mp3' doesn't start with an ID3 tag

I think, it there be good, if in such a case python-rgain writes the id3-Tag before storing the replay gain value, or give a defined error.

This bug is also reported here:
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=798137

It may be an alternative to take mp3gain in the repos until this bug is fixed?

It affects ubuntu 14.4/16.4
Version of rgain in 14.4 is replaygain 1.2

Regards